Solution.cpp

class Solution {
public:
    bool validTicTacToe(vector<string>& board) {
        auto count = [&](char x) {
            int ans = 0;
            for (auto& row : board)
                for (auto& c : row) ans += c == x;
            return ans;
        };
        auto win = [&](char x) {
            for (int i = 0; i < 3; ++i) {
                if (board[i][0] == x && board[i][1] == x && board[i][2] == x) return true;
                if (board[0][i] == x && board[1][i] == x && board[2][i] == x) return true;
            }
            if (board[0][0] == x && board[1][1] == x && board[2][2] == x) return true;
            return board[0][2] == x && board[1][1] == x && board[2][0] == x;
        };
        int x = count('X'), o = count('O');
        if (x != o && x - 1 != o) return false;
        if (win('X') && x - 1 != o) return false;
        return !(win('O') && x != o);
    }
};