Question

794. Valid Tic-Tac-Toe State

中文文档

Description

Given a Tic-Tac-Toe board as a string array board, return true if and only if it is possible to reach this board position during the course of a valid tic-tac-toe game.

The board is a 3 x 3 array that consists of characters ' ', 'X', and 'O'. The ' ' character represents an empty square.

Here are the rules of Tic-Tac-Toe:

• Players take turns placing characters into empty squares ' '.
• The first player always places 'X' characters, while the second player always places 'O' characters.
• 'X' and 'O' characters are always placed into empty squares, never filled ones.
• The game ends when there are three of the same (non-empty) character filling any row, column, or diagonal.
• The game also ends if all squares are non-empty.
• No more moves can be played if the game is over.

 

Example 1:

Input: board = ["O  ","   ","   "]
Output: false
Explanation: The first player always plays "X".

Example 2:

Input: board = ["XOX"," X ","   "]
Output: false
Explanation: Players take turns making moves.

Example 3:

Input: board = ["XOX","O O","XOX"]
Output: true

 

Constraints:

• board.length == 3
• board[i].length == 3
• board[i][j] is either 'X', 'O', or ' '.

Solutions

Solution 1

class Solution:
  def validTicTacToe(self, board: List[str]) -> bool:
    def win(x):
      for i in range(3):
        if all(board[i][j] == x for j in range(3)):
          return True
        if all(board[j][i] == x for j in range(3)):
          return True
      if all(board[i][i] == x for i in range(3)):
        return True
      return all(board[i][2 - i] == x for i in range(3))

    x = sum(board[i][j] == 'X' for i in range(3) for j in range(3))
    o = sum(board[i][j] == 'O' for i in range(3) for j in range(3))
    if x != o and x - 1 != o:
      return False
    if win('X') and x - 1 != o:
      return False
    return not (win('O') and x != o)

class Solution {
  private String[] board;

  public boolean validTicTacToe(String[] board) {
    this.board = board;
    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);
  }

  private boolean win(char x) {
    for (int i = 0; i < 3; ++i) {
      if (board[i].charAt(0) == x && board[i].charAt(1) == x && board[i].charAt(2) == x) {
        return true;
      }
      if (board[0].charAt(i) == x && board[1].charAt(i) == x && board[2].charAt(i) == x) {
        return true;
      }
    }
    if (board[0].charAt(0) == x && board[1].charAt(1) == x && board[2].charAt(2) == x) {
      return true;
    }
    return board[0].charAt(2) == x && board[1].charAt(1) == x && board[2].charAt(0) == x;
  }

  private int count(char x) {
    int cnt = 0;
    for (var row : board) {
      for (var c : row.toCharArray()) {
        if (c == x) {
          ++cnt;
        }
      }
    }
    return cnt;
  }
}

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);
  }
};

func validTicTacToe(board []string) bool {
  var x, o int
  for _, row := range board {
    for _, c := range row {
      if c == 'X' {
        x++
      } else if c == 'O' {
        o++
      }
    }
  }
  win := func(x byte) bool {
    for 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
  }
  if x != o && x-1 != o {
    return false
  }
  if win('X') && x-1 != o {
    return false
  }
  return !(win('O') && x != o)
}

/**
 * @param {string[]} board
 * @return {boolean}
 */
var validTicTacToe = function (board) {
  function count(x) {
    let cnt = 0;
    for (const row of board) {
      for (const c of row) {
        cnt += c == x;
      }
    }
    return cnt;
  }
  function win(x) {
    for (let 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;
  }
  const [x, o] = [count('X'), count('O')];
  if (x != o && x - 1 != o) {
    return false;
  }
  if (win('X') && x - 1 != o) {
    return false;
  }
  return !(win('O') && x != o);
};