# 问题 原题链接：[https://leetcode.com/problems/design-tic-tac-toe/](https://leetcode.com/problems/design-tic-tac-toe/) Design a Tic-tac-toe game that is played between two players on a n x n grid. You may assume the following rules: A move is guaranteed to be valid and is placed on an empty block. Once a winning condition is reached, no more moves is allowed. A player who succeeds in placing n of their marks in a horizontal, vertical, or diagonal row wins the game. Example: ``` Given n = 3, assume that player 1 is "X" and player 2 is "O" in the board. TicTacToe toe = new TicTacToe(3); toe.move(0, 0, 1); -> Returns 0 (no one wins) |X| | | | | | | // Player 1 makes a move at (0, 0). | | | | toe.move(0, 2, 2); -> Returns 0 (no one wins) |X| |O| | | | | // Player 2 makes a move at (0, 2). | | | | toe.move(2, 2, 1); -> Returns 0 (no one wins) |X| |O| | | | | // Player 1 makes a move at (2, 2). | | |X| toe.move(1, 1, 2); -> Returns 0 (no one wins) |X| |O| | |O| | // Player 2 makes a move at (1, 1). | | |X| toe.move(2, 0, 1); -> Returns 0 (no one wins) |X| |O| | |O| | // Player 1 makes a move at (2, 0). |X| |X| toe.move(1, 0, 2); -> Returns 0 (no one wins) |X| |O| |O|O| | // Player 2 makes a move at (1, 0). |X| |X| toe.move(2, 1, 1); -> Returns 1 (player 1 wins) |X| |O| |O|O| | // Player 1 makes a move at (2, 1). |X|X|X| ``` Follow up: - Could you do better than O(n2) per move() operation? # 分析过程 - 输入：下棋的位置 - 输出：棋盘情况，胜负情况 - 思路：两个选手，一个下棋时记录为 1，一个记录为 -1，判定胜负的方法为：每一行、每一列、对角线的值累加，为 n 或 -n，即游戏结束，否则游戏继续。 # 解决方法 ```swift class TicTacToe { var board = [[Int]]() var n: Int { return board.count } /** Initialize your data structure here. */ init(_ n: Int) { for _ in 0..<n { board.append([Int].init(repeating: 0, count: n)) } } /** Player {player} makes a move at ({row}, {col}). @param row The row of the board. @param col The column of the board. @param player The player, can be either 1 or 2. @return The current winning condition, can be either: 0: No one wins. 1: Player 1 wins. 2: Player 2 wins. */ func move(_ row: Int, _ col: Int, _ player: Int) -> Int { let playerToValue = [1 : -1, 2 : 1] board[row][col] = playerToValue[player]! return vaildBoard(row: row, col: col) ? player : 0 } // 检查棋盘，返回 true 代表游戏结束 internal func vaildBoard(row: Int, col: Int) -> Bool { // 行 do { let sum = board[row].reduce(0) { $0 + $1 } if sum == n || sum == -n { return true } } // 列 do { var sum = 0 for field in 0..<n { sum += board[field][col] } if sum == n || sum == -n { return true } } // 扫描对角线 var sum = 0 for i in 0..<n { sum += board[i][i] if sum == n || sum == -n { return true } } sum = 0 for i in 0..<n { sum += board[n - 1 - i][i] if sum == n || sum == -n { return true } } return false } } ```