Leetcode Flip Game

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 twoconsecutive "++" 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 compute all possible states of the string after one valid move.

For example, given s = "++++", after one move, it may become one of the following states:

[
  "--++",
  "+--+",
  "++--"
]

If there is no valid move, return an empty list [].

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解题思路：

看清题意，目的是“Write a function to compute all possible states of the string after one valid move.” 找出有效移动一次后的所有可能结果。那么只要能找出连续的“++”，加上前面的和后面的，就得到了一个结果。

Complexity: O(n)

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Java code:

public class Solution {
    public List<String> generatePossibleNextMoves(String s) {
        List<String> result = new ArrayList<String>();
        for(int i = 1; i< s.length(); i++){
            if(s.charAt(i-1) == '+' && s.charAt(i) == '+'){
                result.add(s.substring(0,i-1) + "--" + s.substring(i+1));
            }
        }
        return result;
    }
}

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Reference:

1. https://leetcode.com/discuss/64335/simple-solution-in-java