This approach will work well until it’s possible to allocate new calls on the stack. And as the number of calls grows exponentially that’s pretty easy to end up with a StackOverflow error. But for these tests, it’s quite enough.
The best in recursion + memorization solution that it’s very intuitive and performs great (when input is limited…))
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So it’s one of those time where I KNOW there is a factorial number of cases, that test case goes up to 100, and yet I still code a greedy algorithm. Like, yeah maybe 100! isn’t as much as last time I checked … 
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I do agree. A relatively simple recursion can do the trick. The problem is the execution time. I have a simple code that finds pretty well the right answer, but that cannot resolve the problem in time when it comes to the last test and I’m a stuck finding an efficient algorithm.
That’s where the dynamic programming comes.
Consider reading this section of the wikipedia article : Dynamic programming - Wikipedia
This really helped me to identify and solve the exercise 
Same for me, the problem is the execution time. I know that I have too much possibilities (and no recursion by the way) 
It succeed till 40 cars, then it fails.
I didn’t success 100% yet. only the last test fail with my code so I’m probably not the best to reply but here is my advice:
become familiar with recursive function
then think of a code that can check every possible cases
then optimise your code with condition to skip useless cases.
Also, when the optimisation is needed, I guess the language choosen is important. I code with Js but it’s not the fastest one…