293. Flip Game

Description

You are playing a Flip Game with your friend.

You are given a string currentState that contains only '+' 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.

Return all possible states of the string currentState after one valid move. You may return the answer in any order. If there is no valid move, return an empty list [].

 

Example 1:

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

Example 2:

Input: currentState = "+"
Output: []

 

Constraints:

  • 1 <= currentState.length <= 500
  • currentState[i] is either '+' or '-'.

Solutions

Solution 1

Python Code
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class Solution:
    def generatePossibleNextMoves(self, currentState: str) -> List[str]:
        s = list(currentState)
        ans = []
        for i, c in enumerate(s[:-1]):
            if c == "+" and s[i + 1] == "+":
                s[i] = s[i + 1] = "-"
                ans.append("".join(s))
                s[i] = s[i + 1] = "+"
        return ans

Java Code
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class Solution {
    public List<String> generatePossibleNextMoves(String currentState) {
        char[] cs = currentState.toCharArray();
        List<String> ans = new ArrayList<>();
        for (int i = 0; i < cs.length - 1; ++i) {
            if (cs[i] == '+' && cs[i + 1] == '+') {
                cs[i] = '-';
                cs[i + 1] = '-';
                ans.add(String.valueOf(cs));
                cs[i] = '+';
                cs[i + 1] = '+';
            }
        }
        return ans;
    }
}

C++ Code
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class Solution {
public:
    vector<string> generatePossibleNextMoves(string currentState) {
        vector<string> ans;
        for (int i = 0; i < currentState.size() - 1; ++i) {
            if (currentState[i] == '+' && currentState[i + 1] == '+') {
                currentState[i] = '-';
                currentState[i + 1] = '-';
                ans.push_back(currentState);
                currentState[i] = '+';
                currentState[i + 1] = '+';
            }
        }
        return ans;
    }
};

Go Code
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func generatePossibleNextMoves(currentState string) []string {
	ans := []string{}
	cs := []byte(currentState)
	for i, c := range cs[1:] {
		if c == '+' && cs[i] == '+' {
			cs[i], cs[i+1] = '-', '-'
			ans = append(ans, string(cs))
			cs[i], cs[i+1] = '+', '+'
		}
	}
	return ans
}