LeetCode 293. Flip Game

原题链接在这里：https://leetcode.com/problems/flip-game/description/

题目：

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 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 [].

题解：

若是连着的"++", 就把这段用"--"替代放到res中.

Note: 当i == s.length()-1走到最后一位时. s.substring(i+1), 不会out of index, 会返回"". 但再大就不行了.

Time Complexity: O(n). Space: O(1) regardless res.

AC Java:

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

 跟上Flip Game II