From fb357810cb87e9f6f556b8013670930c66f93ef0 Mon Sep 17 00:00:00 2001
From: tphyhFighting <2363176358@qq.com>
Date: Thu, 9 Dec 2021 13:26:30 +0800
Subject: [PATCH] add: leetcode 0794 readme

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+# [794. Valid Tic-Tac-Toe State](https://leetcode-cn.com/problems/valid-tic-tac-toe-state/)
+
+## 题目
+
+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**:
+
+![https://assets.leetcode.com/uploads/2021/05/15/tictactoe1-grid.jpg](https://assets.leetcode.com/uploads/2021/05/15/tictactoe1-grid.jpg)
+
+    Input: board = ["O  ","   ","   "]
+    Output: false
+    Explanation: The first player always plays "X".
+
+**Example 2**:
+
+![https://assets.leetcode.com/uploads/2021/05/15/tictactoe2-grid.jpg](https://assets.leetcode.com/uploads/2021/05/15/tictactoe2-grid.jpg)
+
+    Input: board = ["XOX"," X ","   "]
+    Output: false
+    Explanation: Players take turns making moves.
+
+**Example 3**:
+
+![https://assets.leetcode.com/uploads/2021/05/15/tictactoe3-grid.jpg](https://assets.leetcode.com/uploads/2021/05/15/tictactoe3-grid.jpg)
+
+    Input: board = ["XXX","   ","OOO"]
+    Output: false
+
+**Example 4**:
+
+![https://assets.leetcode.com/uploads/2021/05/15/tictactoe4-grid.jpg](https://assets.leetcode.com/uploads/2021/05/15/tictactoe4-grid.jpg)
+
+    Input: board = ["XOX","O O","XOX"]
+    Output: true
+
+**Constraints:**
+
+- board.length == 3
+- board[i].length == 3
+- board[i][j] is either 'X', 'O', or ' '.
+
+## 题目大意
+
+给你一个字符串数组 board 表示井字游戏的棋盘。当且仅当在井字游戏过程中，棋盘有可能达到 board 所显示的状态时，才返回 true 。
+
+井字游戏的棋盘是一个 3 x 3 数组，由字符 ' '，'X' 和 'O' 组成。字符 ' ' 代表一个空位。
+
+以下是井字游戏的规则：
+
+- 玩家轮流将字符放入空位（' '）中。
+- 玩家 1 总是放字符 'X' ，而玩家 2 总是放字符 'O' 。
+- 'X' 和 'O' 只允许放置在空位中，不允许对已放有字符的位置进行填充。
+- 当有 3 个相同（且非空）的字符填充任何行、列或对角线时，游戏结束。
+- 当所有位置非空时，也算为游戏结束。
+- 如果游戏结束，玩家不允许再放置字符。
+
+## 解题思路
+
+分类模拟：
+- 根据题意棋盘在任意时候，要么 X 的数量比 O 的数量多 1，要么两者相等
+- X 的数量等于 O 的数量时,任何行、列或对角线都不会出现 3 个相同的 X
+- X 的数量比 O 的数量多 1时,任何行、列或对角线都不会出现 3 个相同的 O
+
+## 代码
+
+```go
+package leetcode
+
+func validTicTacToe(board []string) bool {
+	cntX, cntO := 0, 0
+	for i := range board {
+		for j := range board[i] {
+			if board[i][j] == 'X' {
+				cntX++
+			} else if board[i][j] == 'O' {
+				cntO++
+			}
+		}
+	}
+	if cntX < cntO || cntX > cntO+1 {
+		return false
+	}
+	if cntX == cntO {
+		return process(board, 'X')
+	}
+	return process(board, 'O')
+}
+
+func process(board []string, c byte) bool {
+	//某一行是"ccc"
+	if board[0] == string([]byte{c, c, c}) || board[1] == string([]byte{c, c, c}) || board[2] == string([]byte{c, c, c}) {
+		return false
+	}
+	//某一列是"ccc"
+	if (board[0][0] == c && board[1][0] == c && board[2][0] == c) ||
+		(board[0][1] == c && board[1][1] == c && board[2][1] == c) ||
+		(board[0][2] == c && board[1][2] == c && board[2][2] == c) {
+		return false
+	}
+	//某一对角线是"ccc"
+	if (board[0][0] == c && board[1][1] == c && board[2][2] == c) ||
+		(board[0][2] == c && board[1][1] == c && board[2][0] == c) {
+		return false
+	}
+	return true
+}
+```
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