Question

Formatted question description: https://leetcode.ca/all/294.html

 294	Flip Game II

 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.

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

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

 Follow up:
    Derive your algorithm's runtime complexity.

Algorithm

The function canWin means “In the current state, there is at least one possible option that can make him/her win”.

Code

Java

public class Flip_Game_II {

    public class Solution {
        public boolean canWin(String s) {
            for (int i = 1; i < s.length(); i++) {
                if (s.charAt(i) == '+' && s.charAt(i - 1) == '+') {

                    // can combine if, but leave it for clarity
                    if (!canWin(s.substring(0, i - 1) + "--" + s.substring(i + 1))) { // @note: after flip, opponent cannot win, then player can win
                        return true;
                    }
                }
            }

            return false;
        }
    }
}

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