题目链接

有效的数独

题目描述

注意点

• board.length == 9
• board[i].length == 9
• board[i][j] 是一位数字（1-9）或者 ‘.’

解答思路

• 首先判断行是否满足数独条件，再判断列是否满足数独条件，最后再判断划分的3x3方格是否满足数独条件，中间有一处不满足则直接返回false，遍历完后都满足条件则返回true

代码

class Solution {
    public boolean isValidSudoku(char[][] board) {
        int row = board.length;
        int col = board[0].length;
        // 判断行
        for (int i = 0; i < row; i++) {
            int[] arr = new int[10];
            for (int j = 0; j < col; j++) {
                if (board[i][j] == '.') {
                    continue;
                }
                if (arr[board[i][j] - '0'] != 0) {
                    return false;
                }
                arr[board[i][j] - '0'] = 1;
            }
        }
        // 判断列
        for (int j = 0; j < col; j++) {
            int[] arr = new int[10];
            for (int i = 0; i < row; i++) {
                if (board[i][j] == '.') {
                    continue;
                }
                if (arr[board[i][j] - '0'] != 0) {
                    return false;
                }
                arr[board[i][j] - '0'] = 1;
            }
        }
        // 判断3 x 3方格
        for (int i = 0; i < row; i = i + 3) {
            for (int j = 0; j < col; j = j + 3) {
                if (!isValidSudokuSquare(board, i, j)) {
                    return false;
                }
            }
        }
        return true;
    }

    public boolean isValidSudokuSquare(char[][] board, int x, int y) {
        int[] arr = new int[10];
        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {
                if (board[x + i][y + j] == '.') {
                    continue;
                }
                if (arr[board[x + i][y + j] - '0'] != 0) {
                    return false;
                }
                arr[board[x + i][y + j] - '0'] = 1; 
            }
        }
        return true;
    }
}

关键点

• 有效数独的条件