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:
boardis 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.
// 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);
}
};
Java
-
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; } } -
// 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); } }; -
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