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Formatted question description: https://leetcode.ca/all/794.html
794. Valid Tic-Tac-Toe State (Medium)
A Tic-Tac-Toe board is given 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, and 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 3 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 = [“XXX”, “ “, “OOO”]
Output: false
Example 4:
Input: board = [“XOX”, “O O”, “XOX”]
Output: true
Note:
board
is a length-3 array of strings, where each stringboard[i]
has length 3.- Each
board[i][j]
is a character in the set{" ", "X", "O"}
.
Solution 1.
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class Solution { public boolean validTicTacToe(String[] board) { int xCount = 0, oCount = 0; for (String row: board) { for (char c: row.toCharArray()) { if (c == 'X') xCount++; if (c == 'O') oCount++; } } if (oCount != xCount && oCount != xCount - 1) return false; if (win(board, 'X') && oCount != xCount - 1) return false; if (win(board, 'O') && oCount != xCount) return false; return true; } public boolean win(String[] B, char P) { for (int i = 0; i < 3; i++) { if (P == B[0].charAt(i) && P == B[1].charAt(i) && P == B[2].charAt(i)) return true; if (P == B[i].charAt(0) && P == B[i].charAt(1) && P == B[i].charAt(2)) return true; } if (P == B[0].charAt(0) && P == B[1].charAt(1) && P == B[2].charAt(2)) return true; if (P == B[0].charAt(2) && P == B[1].charAt(1) && P == B[2].charAt(0)) return true; return false; } } ############ 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; } }
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// OJ: https://leetcode.com/problems/valid-tic-tac-toe-state/ // Time: O(1) // Space: O(1) class Solution { private: int count(vector<string>& board, char target){ int cnt = 0; for (auto row : board) { for (char c : row) { if (c == target) ++cnt; } } return cnt; } bool testWin(vector<string>& board, char target) { for (int i = 0; i < 3; ++i) { for (int j = 0; j < 3; ++j) { if (board[i][j] != target) break; if (j == 2) return true; } } for (int i = 0; i < 3; ++i) { for (int j = 0; j < 3; ++j) { if (board[j][i] != target) break; if (j == 2) return true; } } for (int i = 0; i < 3; ++i) { if (board[i][i] != target) break; if (i == 2) return true; } for (int i = 0; i < 3; ++i) { if (board[i][2 - i] != target) break; if (i == 2) return true; } return false; } public: bool validTicTacToe(vector<string>& board) { int xCnt = count(board, 'X'); int oCnt = count(board, 'O'); if (xCnt != oCnt && xCnt != oCnt + 1) return false; bool xWin = testWin(board, 'X'); bool oWin = testWin(board, 'O'); if (xWin && oWin) return false; if (!xWin && !oWin) return true; return (xWin && xCnt == oCnt + 1) || (oWin && xCnt == oCnt); } };
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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: def validTicTacToe(self, board): """ :type board: List[str] :rtype: bool """ xCount, oCount = 0, 0 for i in range(3): for j in range(3): if board[i][j] == 'O': oCount += 1 elif board[i][j] == 'X': xCount += 1 if oCount != xCount and oCount != xCount - 1: return False if oCount != xCount and self.win(board, 'O'): return False if oCount != xCount - 1 and self.win(board, 'X'): return False return True def win(self, board, P): # board is list[str] # P is 'X' or 'O' for two players for j in range(3): if all(board[i][j] == P for i in range(3)): return True if all(board[j][i] == P for i in range(3)): return True if board[0][0] == board[1][1] == board[2][2] == P: return True if board[0][2] == board[1][1] == board[2][0] == P: return True return False
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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) }
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/** * @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); };