294. (locked)Flip Game II

Difficulty: Medium

Frequency: N/A

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.


My solution:
Data structure:
string, backtracking
Steps:
Complexity:
Runtime:
Space:
Test cases:
Corner cases:
Code:
class Solution {
public:
    bool canWin(string s) {
        for (int i = -1; i = s.find("++", i + 1) >= 0; ) {
            if(!canWin(s.substr(0, i) + "--" + s.substr(i + 2)))
                return true;
        } 
        return false;
    }
}

Another solution:
Data structure:
steps:
Complexity:
Runtime:
Space:
Code:

Things to learn:
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