[LeetCode] Flip Game II

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You are playing the following Flip Game with your friend: Given a string that contains only these two characters: + and -, you and your friend take turns to flip two consecutive "++" into "--". The game ends when a person can no longer make a move and therefore the other person will be the winner.

Problem Description:

The simplest solution that I have found is here (refer to the first paragraph for explanations of the idea and the Java code). I rewrite it in C++.

Follow up:

Derive your algorithm's runtime complexity.

The idea is very straightforward: if you can make s non-winnable by a move, then you will win.

For example, given s = "++++", return true. The starting player can guarantee a win by flipping the middle "++" to become "+--+".

If you are interested to learn more, this post shares a more sophisticated solution using game theory (it reduces the running time to 0 seconds!). The code is restructured as below.

Write a function to determine if the starting player can guarantee a win.