[Swift]LeetCode794. 有效的井字游戏 | Valid Tic-Tac-Toe State

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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 string board[i] has length 3.
• Each board[i][j] is a character in the set {" ", "X", "O"}.

---

用字符串数组作为井字游戏的游戏板 board。当且仅当在井字游戏过程中，玩家有可能将字符放置成游戏板所显示的状态时，才返回 true。

该游戏板是一个 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。
• 第一个玩家总是放字符 “X”，且第二个玩家总是放字符 “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。

示例 1:
输入: board = ["O  ", "   ", "   "]
输出: false
解释: 第一个玩家总是放置“X”。

示例 2:
输入: board = ["XOX", " X ", "   "]
输出: false
解释: 玩家应该是轮流放置的。

示例 3:
输入: board = ["XXX", "   ", "OOO"]
输出: false

示例 4:
输入: board = ["XOX", "O O", "XOX"]
输出: true

说明:

• 游戏板 board 是长度为 3 的字符串数组，其中每个字符串 board[i] 的长度为 3。
•  board[i][j] 是集合 {" ", "X", "O"} 中的一个字符。

---

Runtime: 8 ms

Memory Usage: 19.9 MB

class Solution {
    func validTicTacToe(_ board: [String]) -> Bool {
        var xwin:Bool = false
        var owin:Bool = false
        var row:[Int] = [Int](repeating:0,count:3)
        var col:[Int] = [Int](repeating:0,count:3)
        var diag:Int = 0
        var antidiag:Int = 0
        var turns:Int = 0
        for i in 0..<3
        {
            for j in 0..<3
            {
                if board[i][j] == "X"
                {
                    row[i] += 1
                    col[j] += 1
                    turns += 1
                    if i == j {diag += 1}
                    if i + j == 2 {antidiag += 1}
                }
                else if board[i][j] == "O"
                {
                    row[i] -= 1
                    col[j] -= 1
                    turns -= 1
                    if i == j {diag -= 1}
                    if i + j == 2 {antidiag -= 1}
                }                
            }            
        }
        xwin = row[0] == 3 || row[1] == 3 || row[2] == 3 ||
               col[0] == 3 || col[1] == 3 || col[2] == 3 ||
               diag == 3 || antidiag == 3
        owin = row[0] == -3 || row[1] == -3 || row[2] == -3 ||
               col[0] == -3 || col[1] == -3 || col[2] == -3 ||
               diag == -3 || antidiag == -3
        if (xwin && turns == 0) || (owin && turns == 1) {return false}
        return (turns == 0 || turns == 1) && (!xwin || !owin)
    }
}

//String扩展
extension String {        
    //subscript函数可以检索数组中的值
    //直接按照索引方式截取指定索引的字符
    subscript (_ i: Int) -> Character {
        //读取字符
        get {return self[index(startIndex, offsetBy: i)]}
    }
}

---

8ms

class Solution {

    func validTicTacToe(_ board: [String]) -> Bool {
        var xW = 0
        var oW = 0
        var numX = 0
        var numO = 0

        for i in 0..<board.count {
            for j in 0..<board[i].count {
                checkSet(board[i][j], &numX, &numO)
            }
            if board[0][i]==board[1][i] && board[1][i]==board[2][i]{
                checkSet(board[0][i], &xW, &oW)
            }

            if board[i][0]==board[i][1] && board[i][1]==board[i][2]{
                checkSet(board[i][0], &xW, &oW)
            }
        }

        if board[0][0]==board[1][1] && board[1][1]==board[2][2]{
            checkSet(board[1][1], &xW, &oW);
        }

        if board[0][2]==board[1][1] && board[1][1]==board[2][0]{
            checkSet(board[1][1], &xW, &oW)
        }
        return (numX==numO && xW==0) || (numX == numO+1 && oW==0)
    }

    func checkSet(_ v: Character, _ x: inout Int, _ o:inout Int) {
        if v == "X"{
            x += 1
        }
        else if v=="O" {
            o += 1
        }
    }
}

extension String{
    subscript(index:Int)->Character{
        return self[self.index(self.startIndex, offsetBy:index)]
    }
}