validTic-Tac-ToeState.py

#! /usr/bin/env python3
# -*- coding: utf-8 -*-

# Source: https://leetcode.com/problems/valid-tic-tac-toe-state/
# Author: Miao Zhang
# Date:   2021-03-11

class Solution:
    def validTicTacToe(self, board: List[str]) -> bool:
        x_count = sum(row.count('X') for row in board)
        o_count = sum(row.count('O') for row in board)
        
        def win(board, player):
            for i in range(3):
                if all(board[i][j] == player for j in range(3)):
                    return True
                if all(board[j][i] == player for j in range(3)):
                    return True
            return player == board[0][0] == board[1][1] == board[2][2] or \
                   player == board[0][2] == board[1][1] == board[2][0]
        
        if o_count not in {x_count - 1, x_count}: return False
        if win(board, 'X') and x_count - 1 != o_count: return False
        if win(board, 'O') and x_count != o_count: return False
        return True