[Community Puzzle] Longest coast

Puzzles
#1

https://www.codingame.com/training/easy/longest-coast

Send your feedback or ask for help here!

Created by @Ayza,validated by @FredericLocquet,@InSync and @Darazdeblek.
If you have any issues, feel free to ping them.

#2

Testcase 4 is tricky, it counts not only surrounding water but also inner lakes

#3

true, surrounding may not be the best word to describe the goal. if you have any better suggestions please let me know. (alternatively I could mention that water inside the island counts)

#4

coast, coastline, seashore waterside, waterfront…

for your selection

1 Like
#5

Thanks, should be better now. changed the title aswell.

#6

Why does test 5 output a coast length of 10, I am (and my code) counting 15…

#7

These are the positions of the blocks belonging to the 3rd island (in format y,x):
[[3, 5],[4, 5],[4, 6],[5, 6],[4, 4],[5, 4]]

Count all the water blocks surrounding them excluding blocks you already counted previously, and you’ll see that they total up to 10.

#8

Don’t count the corners, just count the EWNS contiguous borders.

#9

nice twist on the classic islands bfs problem. Makes you work a bit more for the answer by testing that you don’t double-count coasts in your bfs, and making a sort on multiple properties.

1 Like
#10

It’s a discrete derivation problem.

#11

Large Archipelago.
“when encountering a block that you haven’t visited”
It’s a bit boring, I was defining an whole island when i met a new block. Seems its not the way to proceed.
I have the good number of water around, but not the good position of the island (56 88 instead of 51 88)

#12

Hello,

I’m having problems with the Validator 1 test, but pass all the others.
Can someone find me good test case so I can debug what is wrong plz?

#13

You can send me your code, I’ll send back what’s wrong.

#14

Hi,
May I have not took the problem in good way, but on my approach it seems more a medium puzzle.
The point of difficulty is to maintain the list of islands in the right order when these are connecting far from their first discovery…

#15

I also had some trouble because I misinterpreted the wanted output

I was sorting the islands by: most amount of earth, then most amount of water, then lowest index
the correct sorting is only: most amount of water, then lowest index

#16

depending on how you iterate through your maps to find islands, finding the position of the island can become really easy - or terribly hard.
It is all a matter of finding the good way to iterate to identify islands :wink:

1 Like