題目描述

請你判斷一個 9x9 的數獨是否有效。只需要 根據以下規則 ，驗證已經填入的數字是否有效即可。

數字 1-9 在每一行只能出現一次。
數字 1-9 在每一列只能出現一次。
數字 1-9 在每一個以粗實線分隔的 3x3 宮內只能出現一次。（請參考示例圖）
數獨部分空格內已填入了數字，空白格用 '.' 表示。

注意：

• 一個有效的數獨（部分已被填充）不一定是可解的。
• 只需要根據以上規則，驗證已經填入的數字是否有效即可。

示例 1：

輸入：
board =
[["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"]]
輸出：true

示例 2：

輸入：
board =
[["8","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"]]
輸出：false
解釋：除了第一行的第一個數字從 5 改為
8 以外，空格內其他數字均與 示例1 相同。 但由於位於左上角的 3x3 宮內有兩個 8 存在, 因此這個數獨是無效的。

來源：力扣（LeetCode）
連結：https://leetcode-cn.com/problems/valid-sudoku
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Java

class Solution {
    public boolean isValidSudoku(char[][] board) {

        int[][] row = new int[9][9];
        int[][] col = new int[9][9];
        int[][][] square = new int[3][3][9];

        for(int i = 0; i < 9; ++i){
            for(int j = 0; j < 9; ++j){
                char c = board[i][j];
                if(c != '.'){
                    int index = c - '0' - 1;

                    row[i][index]++;
                    col[j][index]++;
                    square[i / 3][j / 3][index]++;

                    if(row[i][index] > 1 || col[j][index] > 1 || square[i / 3][j / 3][index] > 1){
                        return false;
                    }
                }
            }
        }
            return true;
    }
    
}