36. Valid Sudoku (Medium)
https://leetcode.com/problems/valid-sudoku/
Determine if a 9x9 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 9
3x3
sub-boxes of the grid must contain the digits1-9
without repetition.
A partially filled sudoku which is valid.
The Sudoku board could be partially filled, where empty cells are filled with the character '.'
.
Example 1:
Input: [ ["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: [ ["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.
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.
- The given board contain only digits
1-9
and the character'.'
. - The given board size is always
9x9
.
Solutions
class Solution {
public boolean isValidSudoku(char[][] board) {
int row = board.length;
int col = board[0].length;
// check rows
for (int i = 0; i < row; i++) {
Set<Character> set = new HashSet<>();
for (int j = 0; j < col; j++) {
if (board[i][j] != '.' && !set.add(board[i][j])) {
return false;
}
}
}
// check columns
for (int i = 0; i < col; i++) {
Set<Character> set = new HashSet<>();
for (int j = 0; j < row; j++) {
if (board[j][i] != '.' && !set.add(board[j][i])) {
return false;
}
}
}
// check sub squares
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
Set<Character> set = new HashSet<>();
for (int x = i * 3; x < i * 3 + 3; x++) {
for (int y = j * 3; y < j * 3 + 3; y++) {
if (board[x][y] != '.' && !set.add(board[x][y])) {
return false;
}
}
}
}
}
return true;
}
}