README_EN.md

293. Flip Game

中文文档

Description

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.

Example:

Input: s = "++++"
Output: 
[
  "--++",
  "+--+",
  "++--"
]

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

Solutions

Python3

class Solution:
    def generatePossibleNextMoves(self, s: str) -> List[str]:
        if not s or len(s) < 2:
            return []
        n = len(s)
        res = []
        for i in range(n - 1):
            if s[i] == '+' and s[i + 1] == '+':
                res.append(s[:i] + "--" + s[i + 2:])
        return res

Java

class Solution {
    public List<String> generatePossibleNextMoves(String s) {
        int n;
        if (s == null || (n = s.length()) < 2) return Collections.emptyList();
        List<String> res = new ArrayList<>();
        for (int i = 0; i < n - 1; ++i) {
            if (s.charAt(i) == '+' && s.charAt(i + 1) == '+') {
                StringBuilder sb = new StringBuilder(s);
                sb.replace(i, i + 2, "--");
                res.add(sb.toString());
            }
        }
        return res;
    }
}

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