技術標籤：leetcode刷題leetcode

有效的數獨

• 題目連結
• 描述
• 示例
• 初始程式碼模板
• 程式碼

題目連結

https://leetcode-cn.com/problems/valid-sudoku/

描述

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。

上圖是一個部分填充的有效的數獨。

數獨部分空格內已填入了數字，空白格用 '.' 表示。


說明:

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。
給定數獨序列只包含數字 1
 
-9 和字元 '.' 。
給定數獨永遠是 9x9 形式的。

示例

示例 1:

輸入:
[
  ["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"]
]

輸出: true

示例 2:

輸入:
[
  ["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。

初始程式碼模板

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

    }
}

程式碼

題目並不難，只是有些繁瑣而已，推薦題解：
https://leetcode-cn.com/problems/valid-sudoku/solution/you-xiao-de-shu-du-by-leetcode/

另外還有更巧妙的解法，使用位運算：
https://leetcode-cn.com/problems/valid-sudoku/solution/java-wei-yun-suan-xiang-jie-miao-dong-zuo-biao-bia/

用陣列基本就可以解決了，map、set什麼的也都可以，不過資料量小，陣列已經足夠。

class Solution {
    public boolean isValidSudoku(char[][] board) {
        int[][] rowArr = new int[9][9];
        int[][] colArr = new int[9][9];
        int[][] boxArr = new int[9][9];

        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                if (board[i][j] == '.') {
                    continue;
                }
                //對應的行陣列
                if (rowArr[i][board[i][j] - '1'] == 1) {
                    return false;
                } else {
                    rowArr[i][board[i][j] - '1'] = 1;
                }

                //對應的列陣列
                if (colArr[j][board[i][j] - '1'] == 1) {
                    return false;
                } else {
                    colArr[j][board[i][j] - '1'] = 1;
                }

                //對應的盒子陣列
                if (boxArr[i / 3 * 3 + j / 3][board[i][j] - '1'] == 1) {
                    return false;
                } else {
                    boxArr[i / 3 * 3 + j / 3][board[i][j] - '1'] = 1;
                }
            }
        }

        return true;
    }
}