Ocean of Code - Feedback & Strategies

So this was almost my 1 year anniversary for playing codingame actively. I started with code a la mode where I spent a day implementing a dijkstra (on a map with 16 or so possibilities) to a be able to have it as a basic algorithm for my bots. For that I am already greatful for codingame to make me a much better developer.
Regarding this particular contest, I found it particularly hard not only because the challenge lasts longer and people were able to come out with great algofrithms but also because of the multiple possible strategies (mine everywhere? silence after mine to entertain uncertainty, toroedo/mine everywhere to get more information about the opponent?)
In the end I couldn’t invest as much time as I would want on this challenge but the key points of my bot (lower rank in legend league) was to:
_determine opp position as well as possible (moves/silence/sonar/torpedo spots/mine trigger sports, damage…)
_hide your position as much as possible (see previous criteria)
_try to not walk into mines (and if you do, spam silence until you get out)
_torpedo/trigger mines only when it’s worth (try to not reveal yourself)
_only surface when you are in a advantageous position (myLife>oppLife but this could certainly be improved)

Overall it was a great challenge that I feel was harder than usual challenges (smaller timeframes, easier to get out of wood/reach legend). But that would be expected during this confinement period where some ppl have a lot of spare time to kill. Overall it was very enjoyable and I am looking forward to the next one!


Here’s my postmortem which only contains my solution, not my personal opinion about the game.

As for how i feel about the game, i honestly didn’t like the game itself. It’s not my type of game and it felt like i need to do too much of an initial write-up just to get started. Definitely disliked that aspect.

I guess it was a good way to fill time for the lockdown period so far.

Some issues with contests in general and not specific to this contest:
I don’t mind the strong wood bots, in fact they are much appreciated if they aren’t nerfed once you commit to beating them. My only issue is that you can’t jump back and forth between wood and bronze. This is troubling because at times you might want to only specific game elements. In this challenge it was perhaps not so much of an issue since you could submit a restricted bot on the ladder and test against it, but i don’t consider that a solution and training offline isn’t the same either. The only other option is to make a smurf each time you want to test something in wood, which isn’t officially allowed.

Also i might want to skip to bronze at the beginning of the contest to see full rules and then jump back to wood to implement one skill at a time.

Another issue is with the leaderboard in general again. There amount of games played should scale based on the amount of people in the league. By the end of the contest gold got very big! Just imagine how the contest would be like if all those 7000 registered players would participate.

I think submits should be more localized, something like playing 50 players above + 50 players below. Only 100 within range anyway.


I finished #89 in Gold (#153 overall) so it looks that I do not written very good bot. What interesting – my bot for some reason – I do not know why - have very good win rate (much bigger that 50%) with Gold Boss. Unfortunately very rarely play with Gold Boss :slight_smile:

I made well only one thing – opponent position prediction. I started with simple bot in Python. I have had plan to port to C++, but never done this. So I have to find a way to do prediction fast. My solution was to work with bits – using Python ability to work on arbitrary big numbers.

I model game board using 256 bits (16 * 16). 16 = 15 points of the arena + 1 point for border. So moves was simply shift (1 or 16) and AND (|) with the bit mask of islands and borders. For each path (stored as bits in integer) I have 1 int with bits representing possible submarine positions. On the start I have 1 path with only 1 point (initial position) and bits on all ocean points. After first move path has 2 points – and in int representing submarine position it was less points after shift and & with bit mask. For all possible moves in SILENT I created new path and int with bits for submarine positions. Sometimes I have had more that few thousands such pairs. To minimise probability of timeout – for big number of such pairs – I use only 0 and 1 move in SILENT. When, for given path, int with positions == 0 – I delete it. If it is no predictions (very rarely – only for opponent with a lot of SILENTs and moves longer that 1) – I wait for SURFACE and start with points from the SURFACE sector.

So deal with TORPEDO, TRIGGER, SONAR, SURFACE is very easy – simply & with corresponding bit map. Because on path I store inf about MINE too – when opponent TRIGGER mine I use this info to predict his position too.

I use TORPEDO or MINE only when I am sure that I will score points. It is easy – using combination of bit shifts and & for possible opponent positions I can find bits corresponding to points for all detonations which can reach all possible opponent positions. If such points are in torpedo range or in mine position – I use torpedo or mine.

I predict my position too. I use it for MOVE calculation – I calculate number of my predicted positions after all possible 2 moves (up to 16 possibilites) – and move in direction with the biggest score function based on number of predicted positions and number of cells which I can reach from new position.

I put mines if possible – in place which add max number of new cells in mines explosion range.

When I decide what to do (MINE + MOVE + TORPEDO + TRIGGER) I predict my position once again. If it is 9 or less possible positions – I add SILENT if possible. Only 1 move – in direction of 2nd MOVE in 2 moves calculations I made for MOVE direction selection.

As you see – I predict opponent position only once – but my position up to 17 times per turn :slight_smile:

Weak points of the bot (points to improve): I do not avoid opponent mines at all, I do not use my SONAR, I do not use my mines to check opponent position, I do not have special moves for fight. So for bot without such things - #89 in Gold and > 50% win rate with Gold Boss – maybe is not as bad as it looks :wink:


This was my second contest, after Unleash The Geek, and I really enjoyed both of them :slight_smile:
I finished #7, and used C++.

The opponent tracker represents half of the code size. The information was stored in 2 separate ways, with for each cell :

  • 2 bit-boards, union of mine positions and remaining free areas for each path ending here,
  • a list of ‘paths’ (in terms of remaining free area and drop positions).

Upon opponent moves, a first filter was applied on the bit-boards, and the ‘paths’ were then updated for the remaining valid cells.
The list of paths was reduced at the end of each turn, merging (not necessarily identical) paths sharing the same mine drops and the same (or a subset of the same) remaining space (a flood-fill was run after each move or silence update). This divided the amount of paths by several orders of magnitude on some situations, without loss of information.
I used a simplified version of Edmonds-Karp’s algorithm to assign triggers to valid mines drop positions at the time of trigger (removing subsets when a perfect match between triggers and drop positions was found).

Each possible opponent cell also had a probability attached. On each move, the number of available neighbors from the starting cell was accumulated for the path. The relative amount between cells’ worst cases was used to assign a probability of presence. This lead to an increase in probability when the opponent ran along islands or edges, or passed through corridors : the cell with the smaller count was very often the cell where the opponent really was :slight_smile: . This however didn’t work so well against a few players who seemed to try to fake their initial position (mimicking island avoidance as is they were on a different part of the map :wink:).
I also used this accumulation counter to decrease probability for non-0 and non-4 silence moves.
These probabilities were useful when considering torpedo shots and triggers, and also for the computation of a danger map (mine drops associated to paths with high probability contributed more).
I thought about taking into account my mine covered area to add some kind of fake islands when doing the accumulation ; it might have increased the efficiency.

The main loop was the following :

  • At the beginning of a turn, I evaluated if an instant kill (or draw) was possible,
  • If not, I ran a MCTS to search for the best move direction (giving bonuses when close to map center, and penalties when above a threshold in danger map, or for scatter loss at depth 1).
    If the score was too low I ran a second search considering silence + move (trying to avoid mines or reduce scatter loss), and eventually, if score was too low again, I ran another one adding surface.
  • Torpedo shots and triggers were then evaluated at each sub position,
  • If available, a silence was added (if it improved my scatter) when opponent was near, or after surface and torpedo shots,
  • Then sonar was triggered if at least 1/3 of opponent scatter could be filtered,
  • At last, a final check could add a last chance torpedo shot (with no associated score threshold) when the opponent could insta-kill us on next turn.

I had plenty of improvements TODOs left, but I instead mostly spent my last days tuning some thresholds and coefficients, which eventually had a substantial impact (for me it wasn’t the log(x)/log(3) mentioned on the chat, but exp(-0.35 * x) :wink:).

Again, many thanks to the authors for this very entertaining contest ! :slight_smile:


Strange, for me it was very easy to start. Maybe because of language I chosen: Python. Disadvantage was that I have had problems with speed in higher leagues.

Evening 1, 1h22m50s: hey, cool topic. Oh, I have to actually implement tracking and torpedoes to get out of the first wood league, with my PC melting down for uncorrelated reasons? Sign me in!

Evening 2, 2h57m50s: reach Wood-1 by completing:

  • basic tracking: starting from full map, maintain set of possible opponent positions.
  • torpedoing: shoot any any cell that has a >0 chance of having an opponent. By “any” I mean furthest reachable (intent: deal more damage than I take). More on that later.
  • movement: nearest unvisited cell, priority to N/S, then W/E. A left-leaning sub.

Evening 3, 2h54m55s: reach Bronze by implementing:

  • SILENCE 0 S whenever I’ve got enough power for it. I power it whenever my torpedo is fully charged yet I don’t know where to shoot.

Evenings 4 (1h40m47s) and 5 (1h31m35s): Make code clean. Eliminate a few “how on earth could it have worked before?” kind of mistakes.

Evening 6, 2h15m37s: end up mid-Silver by:

  • moving with the depth-1 tron heuristic
  • restrict torpedoing to when opponent cover is less than 20 cells and shot won’t harm me. If you followed correctly with the previous heuristic, you’ll notice I could (and would!) torpedo myself a lot before that.

One of those evenings happens to be on the same day as another’s: IIRC I split the stream when I passed a league once.

This sums up nicely to 12h53m34s worth of coding.

Tagging @leojean890 for the next PM.

Thanks a lot @eulerscheZahl and @Illedan for the last-minute work on this!


two mcts :heart_eyes:

1 Like

Finished #11 and very happy with this result!
(would’ve been happier if I made top10 but hey, it’s already my best result anyway!)

Some parts of my bot are pretty much the same as what has already been detailed above, some are more esoteric.
It can be split into 3 main components: Tracking, Pathing and Evaluation

1. Tracking

This is probably the least original part, as everybody pretty much had the same features.
I would assume the opponent could start anywhere that’s not an island and then track his path, removing any that wasn’t possible.
The same would be applied to myself for being able to evaluate how stealthy I’m being.

I chose to represent a path as an array of 16 ints (32 bits).
Each of the first 15 int represented a row, in which the first 15 bits where visited tiles in the row, and the next 15 bits where positions a mine was layed, if any (more on this later).
The last int was position.

  • After each MOVE, TORPEDO or TRIGGER, the paths that are impossible (moving into an island or out of the map, out of range for torpedo, couldn’t have layed a mine there) are removed.
  • After each SILENCE, I duplicate every existing path and from those create new paths to represent every valid silence possibility.
  • After each SURFACE, the visited tiles of every possible path are reset (but not the mine component of the paths!) and the out-of-sector paths removed.
  • After getting SONARed, TORPEDOed or TRIGGERed, the appropriate paths would be removed based on what positions are impossible given the results.

For the opponent, this was done at the beginning of the turn when processing his orders and would typically be very fast.
For myself, this was done when simulating order combinations and would typically take most of the evaluation time (more on this further down).

What went wrong with that:
Since SILENCE makes the number of possible paths dramatically explode, I had to implement a cuttoff at which I would reset my tracking by creating a new set of paths from the opponent’s possible positions.
Doing this however would also make me lose track of his possible mines, obviously not ideal, but thankfully that cutoff was hardly every reached except against chain-silencers.
To avoid timing myself out as well, I would also have a cutoff at which I would simply not consider silencing, based on the assumption that if I’ve got a gazillion paths, I probably don’t need to anyway.
HOWEVER, the GC being what it is, I would still sometimes timeout when the number of paths got close to the cutoffs.

TRIGGER tracking the way I was doing it (with just one bit for marking a position from which a mine is layed) has one obvious shortcoming: it is perfectly valid for someone to lay a mine, go elsewhere, surface, come back and lay another mine from the same position.
This is impossible to handle with my chosen bitboard, so I pretty much simply chose not to based on the fact it didn’t happen very often. I still prevented my tracking from removing paths based on TRIGGERs if there was any doubt to avoid completely losing track of the opponent in those rare cases.

It is also possible for a given mine to be layed from multiple different positions in a given path, making it impossible to know which mine laying position to remove.
In that case, I simply consider that all mines are still there based on the better safe than sorry principle.

2. Pathing

I basically didn’t have any pathing algorithm, instead I though I’d evaluate how good every potential position I finish my turn in is.
To do this I used a BFS of my next 4 MOVE actions (didn’t take SILENCE into account in that depth search), and for each depth I would score with a decaying factor the position based on available space and the probability of a mine being there.

  • Available space is the maximum result of floodfills from every accessible tile around my current position.
  • Probability of a mine being there is defined as the sum of the mine laying positions (divided by the number of mines that can be laid from that position) from which a mine that can reach could’ve been laid, divided by the number of possible paths of the opponent.
    (This is definitely not proper probabilities, but close enough to get the job done)

All of this with some magic coefficients would allow me to score the value of that position.

What went wrong with that:
Mostly everything. Obviously my bot couldn’t see what was further than 4 tiles away and so would sometimes take a turn that will in 5 turns or more lead it to some dead-end or more often into a minefield and certain death.
Likewise because there was no proper pathing, it would sometimes make a small loop, SURFACE and do a similar loop again, just because it doesn’t see problems that are too far away.
This was probably the worst part of my bot and made me lose many games in silly ways.

3. Evaluation

While my tracking was pretty standard (everybody had those features) and my pathing was clearly below average, I think this part is what made my bot stand out.

Every turn, after processing the opponents orders, I would start by establishing a list of my possible orders that “made sense”, based on some heuristic rules and the state of my cooldowns.
The rules for valid order combinations were:
Only MOVE was mandatory, everything else is optional.

For TRIGGER and TORPEDO, I only consider the best possible one from my position at that time, based on the opponent’s possible positions.
“best” is defined as the amount of guaranteed damage that this TRIGGER or TORPEDO will do, which can be 0, 1, 1.5 or 2.
1.5 damage is a guaranteed 1 damage blast that also hits a possible ennemy position, as that is obviously better than a blast that covers all ennemy positions but hits none of them.

For TORPEDO before moving and TRIGGER, I actually disallowed anything that doesn’t hit at least every ennemy position minus one (I allowed for just a little bit of tolerance).
TORPEDO after moving had to hit every ennemy position (damage>=1); it’s stricter because it also usually puts you at a charge disavantage in case of return fire, so better not miss.

This bit of heuristic allowed me to only consider one TRIGGER per turn (since it only happens before moving), and one TORPEDO per MOVE/SILENCE option, dramatically reducing branching.

Next I would just simulate all of those order combinations and evaluate the result as such:

	if (damage >= opponent.life)
	score = (the scoring of the depth search as explained in the previous section)
	if (hasNotSilenced)
		score += (some function based on the number of my positions according to my self-tracking)
	if (hasNotSurfaced)
		score += (some function based on the numer of available tiles)
	score += (some function based on the damage done from trigger and torpedo, if any)
	score -= (some function based on the probability of getting a torpedo in the face)
	return score

Probability of torpedo in the face is defined as the number of paths that the ennemy can shoot at me from, divided by his total number of possible paths (now that’s proper probabilities!)
Or zero if his cooldown is not up, assuming that the opponent always charges his torpedo as a first priority.

Note that removing the bonus based on my number of possible positions when the order combination includes a SILENCE, or the number of available tiles in case of a SURFACE, is my way to assign a cost to those actions.
It turns out to pretty naturally balance itself out: the more detected you get, the less a SILENCE costs. The less space you have, the less a SURFACE costs.
And of course the depth search and torpedo in the face parameter can also make those actions more likely as silencing to a more favorable location will reduce/remove those penalties.

Finally, the first condition make killshots happen very naturally as well.

What went wrong with that:
Not a whole lot to be honest, I feel like this is the part that works. It can be hard to balance out all of the parameters properly, but I think I managed. My pathing was often the death of me, but the eval itself tended to take the right decisions.
One thing I tried to improve towards the end was to allow for more order combinations. For instance, always doing MOVE before SILENCE will usually give you access to the same positions as SILENCE and then MOVE, except in those rare cases where the islands are set up just so.
That didn’t seem to add anything of value and more branching though, so in the end I just scratched that.

So there you go, that’s about all of my 600 LoC explained.
There’s a bunch I could’ve done better, but I’m very happy with the end result!
Thanks to everyone who made this contest happen, I had a lot of fun with it!


BlitzProg, 399th.

I haven’t much to say original about my AI this challenge - It does what you expect from a mid-gold player. I was too busy so I invested only what was necessary to enter the gold league, then I dropped out, because I have other things to do (another challenge and other very distracting real life events). This is a bit sad tho, because I started to like the challenge near the end. I need more lives to do everything I want!

  1. I allocate 4096 possibilities for me, and 4096 for the opponent. each possibility has a visit map, which is stored in a array of 15 ints (I guess many people had this idea)

  2. when the possibilities for the opponent shorten, i start charging torpedo, else I charge silence + mines. I lay mines behind me and trigger the mines when there is a good chance the opponent is here.

  3. I try to move in a way there are as many tiles as possible left for me to move on (so if there is a path to the left and another to the right but the right path is only a few tiles left before I must surface, I probably won’t go there) - while still trying to obfuscate where I could be. when my possibilities shorten too much, I try a silence.

This is enough to reach top Silver.

  1. I search for silence targets. That is, a possible target that uses silences that are always the same distance (Silver boss that always do a Silence 0 / players that only use Silence 1 (direction). If almongst the possibility there is one and only one where it is all Silence 0 (direction) or Silence 1 (direction), it immediately becomes my silence target. This is almost opportunity free and harshly punishes predictable players.

And with that, I was sitting happily in the gold league once again. :slight_smile:

Thanks for the challenge, and thanks for the chat for teaching me how to read STDIN in C++ to relieve my pain of reading many commands in a single line. Yup, I didn’t know how to do that before!


I really enjoyed doing this … and I feel like I’ve learned a lot. Since this was my first time doing a contest, I don’t really feel I got a lot to say on the game itself because the whole thing is new to me and have nothing to compare it to. The only thing I’d like to comment on was the leaderboard. I found it hard to search by schools. Frequently, I tried putting in my school and got no results. I also put in some other school that I saw right there in the leaderboard, and again, got no results. The search just didn’t seem to work. I wanted to see if there were any more participants from my school so I could see how they were doing but I couldn’t. When I did the “Top 100” for schools, it only showed like 37 schools. The other thing I was confused on with the schools was did these people who were in a school group join a group together or where they automatically merged because they had the same school? I am trying to get a couple of my alumni buds to join the next one but I want to make sure we can see how we are doing and not get left out of the mix.

But the contest itself was enjoyable and I am looking forward to the next one.


Hey, here is my quick PM after this contest where I reached #259 (Mid gold).


  • I started using Scala, I implemented a basic tracking with positions to get from wood to bronze, it was enough to get an almost bug-less set of positions where enemy was even if I didn’t consider everything (visited path to reduce even more).
  • Quickly I discovered JVM was pretty bad for quick response due to warmup. I didn’t want to warmup individually each function so I decided to change language and pick Haskell for many reasons: an eleguant, compiled, pure FP and strongly typed language. It took me ~2 days to recode everything. Not a big deal even if I’m quite new to contest in Haskell. My Scala code was already very FP and I got the same exact results with almost no timeouts.
  • I used a BFS called for each neighbor, taking the one that could led to furthest cell. It’s enough to avoid traps, even if it sometimes create suboptimal path.
  • I decided to totally ignore mines (owned by opponent or me), my goal was to reach gold without because I’m lazy and it seemed fun.
  • I used a mean deviation to decide if enemy candidates were packed enough (I prefer 6 candidates all very close from each other rather than 2 distant by 6 cells …). If it was packed enough I would shoot the center. I thought it was pretty clever.
  • Spawn at center of map

How to get to gold

  • I really wanted 0 timeouts so I dug into some black magic for high performance: IOUArray, {-# UNPACK #-} and !bangs (thanks Stilgart and JBM for all your help). Also it is necessary to pick the best data structure for the need (Map, Set, Array etc …). I spent a lot of time replacing everything and pushing in arena without noticing any difference. I spent time coding a bitstream to export a full state to execute it locally and target the slowest function with profiteur.
  • It was necessary to track visited cells (using a Set) instead of just position to reduce candidates even more. Surprisingly performances have not been too much impacted as long as you use a lot of sonars :-).
  • Replacing mean deviation by a scan to find the center of a 3x3 square that would lead to at least 1 damage was really useful and simple.
  • I coded what is described by other as FATALITY but using it even for 1 damage without kill. It combines MOVE, SILENCE and TORPEDO. I allow taking damage if I am sure to deal more damages than I receive.
  • Use sonar if I don’t know at all where enemy is and candidates are in more than 1 sector. Pick the sector with most candidates.
  • Use self-tracking, if less than 20 candidates replace MOVE N by SILENCE N 1. Not sure if SILENCE 0 would be better, didn’t try.

What I did wrong

  • Spending a LOT of time doing nothing, watching replays without really analyzing. Next time I will read Bob advices again.
  • I still didn’t use a proper eval, rather a sort by very few criteria in tuple (+diffDmg, +dealed, -actionsLength).
  • I didn’t use a fancy algorithm like MC(TS) or minmax even if time was really long enough.
  • Ignoring mines is dangerous. Ignoring things is dangerous in general.
  • Didn’t code a nice spawn (avoid small water areas).


I’m not sure to pick Haskell for a next contest if I need REALLY high performance because it can quickly get very complicated and C++ is still a beast (I will probably try Rust). Anyway the resulting 600 LOC are pretty clean, readable and safe!

It was a very nice contest, thanks! The tracking was a barrier for some newcomers I think, but it was interesting to solve. Overall you can build a simple and efficient strategy and have a lot of fun!


Thank you for the competition, really glad that this was released during the outbreak. :slight_smile:

Language: Typescript / Final place 109

Highlights of the game strategy

Tracking the enemy

Since neither player knows the opponent’s starting location it was crucial to have a system that tracks the opponent’s movements and possible locations.

In order to achieve that at the start of the game I loop through the map cells and create a phantom submarine on each empty water cell. At the beginning of each turn I loop through these phantom submarines and filter them based on my and the opponent's commands.

This got tricky with the introduction of the silence command at the later levels, because that is the only command that increases the number of possbile locations.

Originally when the opponet was using the silence command I created copies of the submarines, but unfortunately this resulted in timeouts, especially with bots that were spamming the silence command. So instead of creating copies, for all the submarines that ended up on the same coordinates after executing the silence command I created a composite of those submarines.

Tracking mine deployment

The mine tracking system went through several iterations and was one of the most difficult parts. The final version looks like this:

  • Every phantom submarine has a mine tracker which is a dictionary for mine ids and coordinates
  • Every time a mine is deployed a new key is created on the mine tracker dictionary (the id of the mine), and that object gets populated with all the coordinates where the mine could be deployed.
  • When a mine is triggered I remove the possible locations from each phantom

This way if a phantom submarine gets eliminated the possbile locations for mines also get eliminated alongside it, and if the opponent executes the silence command, the mineTrackers get merged.

Decision making

Basically the way my AI works is it loops through a list of command sets grouped together and chooses one command from each set if the utility is above a certain threshold.

command set example:

  2. [TORPEDO]
  3. [MOVE]
  4. [TORPEDO]
  6. [SILENCE]

If a command was already chosen from a previous set then it skips that calculation.

The utility calculation for each command is a combination of smaller reusable utility functions (e.g. calculateDesireToHideUtility, calculateFireTorpedoAtCoordinatesUtility) .

Looking back at the challenge I wish I did something simpler that would have allowed easier tweaking, but was curious of what could come out of this approach.


Overall I was more satisfied with the bot than not, I wish I could get with it to the highest Legend league, but that is for the next challenge.

Parts of the code that I am proud of

  • The code that tracks the possible locations for the opponent and mines came together nicely
  • The smaller utility functions that were the core building blocks in the decision making

Parts of the code that I am dissatisfied with

  • Although the building blocks for the utility AI were in place, the actual implementation for decision making had its “issues”.

I still need to study a lot more on how to write the part of the AI that makes the actual decisions :smiley:

Again, thanks for the competition!

  • This was really exciting contest, a great, deep game with many opportunities to improve code and learn something new. Big thanks for the contest’s creators!
  • I finished #56 in Legend. I am really happy with the result, and finally getting into Legend after two days of trying to get above top 30 Gold, and to fight the Boss, was a huge relief!
  • My bot is #1 haskell, purely functional, no IOUArray and similar magic, just Vectors, Sets and Maps. It is quite similar to many algorithm features already explained by others, so I will only touch what’s different.
  • Opponent tracking was very elegant and precise, about 100 LOC, also very efficient. It worked surprisingly well with haskell’s persistent data structures and lazy valuation: creating new “variants” of reality was very cheap, as no new maps/tracks are created; pruning impossible tracks was very easy. I only had to start collapsing possible tracks when I started tracking opponent’s intel on me, no performance problems before.
  • In-house game simulation was a big factor in my last day attack on Gold boss. I implemented all the rules during the first week and since that I was testing all new features/versions against a set of previous versions. I tested 1000 pairs of games, and it was a good predictor ob bot’s performance during submission, despite the fact that both algorithms were similar.
  • With my own simulation, I also tried very interesting research on how many moves decide the game. Two bots (bot1 and bot2) with slightly different coefficients were playing games, and when bot1 wins I tried to understand, how many moves should bot2 do differently (using bot1’s coefficients) to revert the game result. Interestingly, 90% of games were decided only by 1 or 2 key moves. Analysing key moves in hundreds of games was insightful to understand, what are key abilities to improve.
  • I spent a week not touching the bot, but trying to use cut-vertices / biconnected component search algorithm in order to have reliable estimation (something better than flood fill) for the next turn. I just could not use randomised path search algorithm due to performance limitations. As some point I gave up with the algo. But on the last day, faced with timeouts problem, I finally implemented it in the right way, and it allowed me to get to Legend.
  • Many hours my computer (not me) spent trying to optimise many algorithm parameters with GA search (all the weights and threshold, which were initially assigned by common sense). To my surprise, 24 hours of optimisation with genetic algorithm, 100Ks of games played - gained nothing, ks0 (initial coefficients) were still optimal! “Don’t spend time playing with constants, implement new features” - this was proved by me. Again.

It finished #6. This contest was really cool, lot of depth so well suited for a 1-month contest. I’m also impressed by the balance of the game considering the conditions it has been created on.

The main parts of my bot are:

Weighted tracking

I record all the paths of the opponent and myself by storing a bitboard of the visited cells and a bitboard of the possible mines placement, and merge them by position if their number is too high, by performing a bitwise AND for the visited cells and a bitwise OR for the mines. At the start of each turn I also perform a merge to produce paths that will be used for the computation part. That way I keep track of every path but only do calculations on a number of paths equal to the number of possible positions, which ensure a low execution time not matter how silence has been spammed.

One thing I added near the end was to give each path a probability. This probability is added when 2 paths are merged, and it changes according to the opponent actions and positions: for example, silences are often performed with 0 or with the maximum possible distance (not necessarily 4), so those paths are given a higher probability. I originally planned to download replays and give weights to actions according to those replays, but I didn’t manage to extract something interesting from them, so I ended up giving random weights for only specific cases (silence and placement). It can probably be widely improved by treating more cases into account than I did, but at least it gave a nice boost for my bot.


SONAR, MINE and TRIGGER are performed with heuristics: mines are placed in order to cover the maximum number of cells (at least n new cells, n decreasing over time). They are triggered if they have a good probability to inflict damage. I only use sonar if the opponent doesn’t have a silence loaded, and if it helps cut a good percentage of paths.

Brute Force

For the other actions I try every possibility of doing (or not doing) the actions in the given order: SURFACE -> TORPEDO -> MOVE -> TORPEDO -> SILENCE -> TORPEDO. When I simulate an action, I also simulate it for all my paths to know which ones are going to be cut. The torpedoes are shot at the cell with the highest probability of dealing damage.

Then, for every opponent path I also do a brute force but without silence (SURFACE -> TORPEDO -> MOVE -> TORPEDO), keeps the best damage they expect to deal, and see what damage it will really deal me. The damage I expect to take back is then the average for all those paths (weighted by the paths probability). This makes my close combat decent, clearly not perfect as I still have some bugs to compute the expected damage I will take (there are corner cases when he can shoot at multiple good places; when he has to surface to inflict more damages will he do it ?..).

This computation was done most of the time in less than 2ms, but was sometimes above 50ms (especially at the start of the game for non-critical actions when there still are a lot of paths) so I just do 1 ply first with a damage back approximation, and keep this result if I don’t have the time for 2 plies.


My evaluation function takes into account:

  • the lives

  • my cooldowns

  • the average damage I expect to deal

  • the average damage I expect to take back

  • the number of positions where I can be

  • the probability of being on a mine (only if I have a low number of positions, otherwise the opponent will never trigger anyway)

  • a flood fill

In the end I don’t have any long term planning at all, the flood fill and trying to maximize the number of paths were just ok to not have something meaningless, but I thing I miss some crucial Elo here… as I do with all the details that are badly implemented, the unoptimized magic numbers, or the features I don’t have… we’re far from mastering this game!

Many thanks to the creators and CG to occupy us on those times, congratulation to the winners, and see you next time!


I will start with a great prise for the authors of the contest. In my opinion it’s one of the best-designed games on CG.

Deep (pun intended), but without using dirty tricks like “you control N entities”; forcing you to directly approach the imperfect information issue (which could be completely ignored in e.g., LOCM), and simultaneously nearly always giving you something more to code and improve - it’s harder to reach the plateau that requires full code rewriting (e.g., need to recode full engine and sim) to improve - nearly on any stages the changes could be done incrementally.

Secondly, thanks to CG for giving us additional leaderboards of School and Companies. Small thing but a great thing. Surely makes competition more appealing for some people, and supports some platform-institution advertisement that goes both ways. CG4Edu!

Also - nice work with copying code straight to multi - although I miss double XP, this removes the artificial burden of downgrading your bot to pass till bronze and other strange cases (some people not resubmitting their bots, etc.). A step in the right direction - definitely.

Few things about my AI.
I ended #119 (Python till silver, than C#), a little bit disappointed. I started making a bot probably at the end of the second week of the contest - when showing OOC during my Institute open days stream.

I had tracker but only based on possible squares occupied by the opponent (or me in case of selftracking), not the paths. But I used some backtracking of moves to work partially as a path tracking. E.g. when opponent surfaces, and I’m updating the assumption he is on a certain square - I backtrack his orders before this silence and mark some squares as visited - thus removing usually nearly half of silence possibilities.

I tried to use a similar technique with the mine tracking - but this was mess, and the results were so noisy and unreliable that I turned this part off (which was probably a mistake).

I really liked the killermove part: I tested all combinations of silence, torpedo, surface, trigger, move to deal the final damage. It required pruning of some redundant combinations as otherwise I had timeouts.

I struggled with the movement strategy, finally I was choosing move (best node on shallow 3 level search) trying to minimize the chance that opponent will track me plus some checks on available water squares (floodfill) and a number of reachable squares in some horizon (BFS). Otherwise, torpedo/mine/trigger before or after the move. With some thresholds on torpedo/triggers expected damage, and the number of water squares/overlay with other mines for mine placement.

Lastly silence, if the opponent pretty much knows where I am. Either defensive (go as far from the opponent as possible when I had very low hp) or just the opposite, try to stick close.

Finally, I ended up in a situation in which I had no clear, easy feature to add, and tuning parameters is a hell, so I submitted on Sunday and went sleep without touching bot in the last minutes ;-). But - if I ever will try to improve my bot for the multi - I already have some ideas thanks to the all great the postmortems posted :wink:

So thank you all for the great challenge and great fun!


Thanks for the great game and posting it to multi so quickly. I was not expecting that to be so fast. Guess that means we can work on it another 16 more days in preparation for the next contest!!

My bot did not make it very far at all. It finished in Wood 1 :sweat_smile: with my two submissions to the contest both having taken place 22 days ago … :man_shrugging: . Only implementing a crude flood-fill for pathing. I had started working on improvements to my pathing but I never finished. I guess I have more time now!!


Great game! It’s awesome that the game worked so well considering how fast it was created.

A bit disappointed by my result (top 400). With the time invested, I was looking to make it to top 200. I think the overall level of bots was better than usual (with 4 weeks, I guess it’s normal).

I deliberately ignored mines (and I complain that I didn’t get top 200 :sweat_smile:) because I wanted to have a very “aggressive” strategy with a few sonars and torpedoes. But enemy early silence commands countered me hard. That was fun anyway :slight_smile:

Thank you for all the kind words and the sharing of your strategies. I hope you’ll enjoy the Spring Challenge 2020 coming soon.

@vbplaya we take into account what’s filled in the player profiles to assign them to their team. For the Spring Challenge 2020, any player will be able to contribute to their school and company. Could you please give me more details in PM about this search issues? (the leaderboard is still available, so we can perhaps reproduce it)


Thanks for the great game, it had all elements to be enjoyable even for 4 weeks!

I started a few days late, but quickly catched up with effective tracking+selftracking combined with heavy use of silence. From silver I was mostly top3 by implementing many ideas first/early. I’m still a bit disappointed with final run where I slowly down from #1 to #4. But it is justice, with many games my winrates were not good enough vs. actual top3. Gratz for them!

Most of the key ideas were already covered in detail multiple times (tracking, floodfill, finisher, damage-probability, mine-danger-map), so I just list them with a couple of less important but interesting heuristics:

  • eval: my turn only with most reasonable action combos/order (prefer silence in the end) + additional heuristics for specific actions
  • scoring: accessible good cells, enemy damage threat, detectability
  • init: biggest lake, 5x5 open area, near center, spiral movement, quick mining
  • mines: least overlap (weakened after surfaces), next to suspected enemy
  • triggering: conservative (except when mines overlap), possible wait for enemy stepping over it
  • enemy tracking probability adjustments: follow of island shapes, silence statistics, mine avoidance, not attacking!, stuck with few cells
  • sonar: charge last, use when it gives the most info (cut states/probability to approx. half)
  • player detection: by behaviour, for key top players, enable/disable some tactics vs. them
  • finisher + check enemy finisher and avoid those positions
  • last resort with no moves (or very last turn as 2nd player): use any action, trigger all mines, even “fire in the dark” or do a low-chance-finisher combo

Thanks for the contest,
It was my big return to the CodinGame. Also I encouraged my daughter to join the contest as well!

I finished in Silver League, but I still have lot of ideas to update my bot :slight_smile:

Thanks again


Can you say a bit more about this ?