36. Valid Sudoku

Problem Statement

Medium

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

Each row must contain the digits 1-9 without repetition.
Each column must contain the digits 1-9 without repetition.
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 '.'.

C++

Source file

class Solution
{
public:
    bool isValidSudoku(vector<vector<char> > &board)
    {
        int used1[9][9] = {0}, used2[9][9] = {0}, used3[9][9] = {0};
        
        for(int i = 0; i < board.size(); ++ i)
            for(int j = 0; j < board[i].size(); ++ j)
                if(board[i][j] != '.')
                {
                    int num = board[i][j] - '0' - 1, k = i / 3 * 3 + j / 3;
                    if(used1[i][num] || used2[j][num] || used3[k][num])
                        return false;
                    used1[i][num] = used2[j][num] = used3[k][num] = 1;
                }
        
        return true;
    }
};

Java

Source file

class Solution {
    public boolean isValidSudoku(char[][] board) {
        int m = board.length, n = board[0].length;
        for (int i = 0; i < m; i++) {
            boolean[] vis = new boolean[10];
            for (int j = 0; j < n; j++) {
                if (board[i][j] == '.')
                    continue;
                if (vis[board[i][j] - '0'])
                    return false;
                vis[board[i][j] - '0'] = true;
            }
        }
        for (int j = 0; j < n; j++) {
            boolean[] vis = new boolean[10];
            for (int i = 0; i < m; i++) {
                if (board[i][j] == '.')
                    continue;
                if (vis[board[i][j] - '0'])
                    return false;
                vis[board[i][j] - '0'] = true;
            }
        }
        for (int g = 0; g < 3; g++) {
            for (int h = 0; h < 3; h++) {
                boolean[] vis = new boolean[10];
                for (int i = 0; i < 3; i++) {
                    for (int j = 0; j < 3; j++) {
                        if (board[g * 3 + i][h * 3 + j] == '.')
                            continue;
                        if (vis[board[g * 3 + i][h * 3 + j] - '0'])
                            return false;
                        vis[board[g * 3 + i][h * 3 + j] - '0'] = true;
                    }
                }
            }
        }
        return true;
    }
}