一、题目原型：

判断一个 9×9 的数独是否有效。只需要根据以下规则，验证已经填入的数字是否有效即可。

数字 1-9 在每一行只能出现一次。
数字 1-9 在每一列只能出现一次。
数字 1-9 在每一个以粗实线分隔的 3×3 宫内只能出现一次。

二、题目意思剖析：

输入:
[
["5","3",".",".","7",".",".",".","."],
["6",".",".","1","9","5",".",".","."],
[".","9","8",".",".",".",".","6","."],
["8",".",".",".","6",".",".",".","3"],
["4",".",".","8",".","3",".",".","1"],
["7",".",".",".","2",".",".",".","6"],
[".","6",".",".",".",".","2","8","."],
[".",".",".","4","1","9",".",".","5"],
[".",".",".",".","8",".",".","7","9"]
]
输出: true

三、解题思路：

数独，应该大家都玩过，其实就只是判断三个点，横、竖、3*3的方格。

func isValidSudoku(_ board: [[Character]]) -> Bool {

    var bool: Bool = true
    
    for i in 0..<board.count {
        
        let characters = board[i]
        var mutCharacters1: [Character] = []
        var mutCharacters2: [Character] = []
        for j in 0..<characters.count {
            
            // 1.每行比较
            let character1 = board[i][j]
            if character1 != "." {
                mutCharacters1.append(character1)
            }
            
            // 2.每列比较
            let character2 = board[j][i]
            if character2 != "." {
                mutCharacters2.append(character2)
            }
            
            if j == characters.count - 1 {
                
                let set1: Set = Set(mutCharacters1)
                if set1.count == mutCharacters1.count {
                    bool = true
                }else {
                    bool = false
                    return bool
                }
                
                let set2: Set = Set(mutCharacters2)
                if set2.count == mutCharacters2.count {
                    bool = true
                }else {
                    bool = false
                    return bool
                }
            }
        }
    }
    
    var index_i = 0
    var index_j = 0
    while index_i<board.count {
        
        // 3.每方格
        while index_j<board[0].count {
            
            var square: [Character] = []
            if board[index_i][index_j] != "." {
                square.append(board[index_i][index_j])
            }
            if board[index_i+1][index_j] != "." {
                square.append(board[index_i+1][index_j])
            }
            if board[index_i+2][index_j] != "." {
                square.append(board[index_i+2][index_j])
            }
            if board[index_i][index_j+1] != "." {
                square.append(board[index_i][index_j+1])
            }
            if board[index_i+1][index_j+1] != "." {
                square.append(board[index_i+1][index_j+1])
            }
            if board[index_i+2][index_j+1] != "." {
                square.append(board[index_i+2][index_j+1])
            }
            if board[index_i][index_j+2] != "." {
                square.append(board[index_i][index_j+2])
            }
            if board[index_i+1][index_j+2] != "." {
                square.append(board[index_i+1][index_j+2])
            }
            if board[index_i+2][index_j+2] != "." {
                square.append(board[index_i+2][index_j+2])
            }
            
            if index_j % 3 == 0 {
                let set: Set = Set(square)
                if set.count == square.count {
                    bool = true
                }else {
                    bool = false
                    return bool
                }
            }
            // 因为是3*3的小方格，所以需要+3，而不是再+1了
            index_j = index_j + 3
        }
        index_i = index_i + 3
        // 因为index_j循环后变成了9，需要设置为0
        index_j = 0
    }
    return bool
}

四、小结

耗时72毫秒，超过73.77%的提交记录，总提交数504。