LeetCode 294: Flip Game II

Explanation:

This problem asks us to determine if the first player can guarantee a win assuming both players play optimally in a game of flipping characters in a string. The rules are that the player can choose any adjacent characters in the string that are "++" and flip them to "--". The game continues until no more moves can be made. To win, the first player needs to make a move that guarantees them a win regardless of the second player's moves.

To solve this problem, we can use a backtracking approach to simulate all possible moves and check if the second player can win from that state. We will keep track of the state of the game using the string representation. If the second player loses in any of the possible states after the first player makes a move, then the first player can win.

• Algorithm:

  1. Iterate through the string and find all occurrences of "++".
  2. For each occurrence, flip the "++" to "--" and recursively call the function with the new string.
  3. If the second player loses in any of the recursive calls, return true (indicating the first player can win).
  4. If all recursive calls result in the second player winning, return false.

• Time Complexity: O(2^N) where N is the length of the input string. In the worst-case scenario, we will have 2^N possible states to check.

• Space Complexity: O(N) for the recursive call stack.

: :

class Solution {
    public boolean canWin(String s) {
        for (int i = 0; i < s.length() - 1; i++) {
            if (s.startsWith("++", i)) {
                String nextState = s.substring(0, i) + "--" + s.substring(i + 2);
                if (!canWin(nextState)) {
                    return true;
                }
            }
        }
        return false;
    }
}