LeetCode-in-Java

36. Valid Sudoku

Medium

Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:

1. Each row must contain the digits 1-9 without repetition.
2. Each column must contain the digits 1-9 without repetition.
3. Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition.

Note:

• A Sudoku board (partially filled) could be valid but is not necessarily solvable.
• Only the filled cells need to be validated according to the mentioned rules.

Example 1:

Input:

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"]]

Output: true

Example 2:

Input:

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"]]

Output: false

Explanation: Same as Example 1, except with the 5 in the top left corner being modified to 8. Since there are two 8’s in the top left 3x3 sub-box, it is invalid.

Constraints:

• board.length == 9
• board[i].length == 9
• board[i][j] is a digit 1-9 or '.'.

Solution

public class Solution {
    private int j1;
    private int[] i1 = new int[9];
    private int[] b1 = new int[9];

    public boolean isValidSudoku(char[][] board) {
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                boolean res = checkValid(board, i, j);
                if (!res) {
                    return false;
                }
            }
        }
        return true;
    }

    private boolean checkValid(char[][] board, int i, int j) {
        if (j == 0) {
            j1 = 0;
        }
        if (board[i][j] == '.') {
            return true;
        }
        int val = board[i][j] - '0';
        if (j1 == (j1 | (1 << (val - 1)))) {
            return false;
        }
        j1 |= 1 << (val - 1);
        if (i1[j] == (i1[j] | (1 << (val - 1)))) {
            return false;
        }
        i1[j] |= 1 << (val - 1);
        int b = (i / 3) * 3 + j / 3;
        if (b1[b] == (b1[b] | (1 << (val - 1)))) {
            return false;
        }
        b1[b] |= 1 << (val - 1);
        return true;
    }
}

This site is open source. Improve this page.