# Sudoku Solver

Write a program to solve a Sudoku puzzle by filling the empty cells.

Empty cells are indicated by the character '.'.

You may assume that there will be only one unique solution.

A sudoku puzzle...

...and its solution numbers marked in red.

https://leetcode.com/problems/sudoku-solver/

Solution :

https://leetcode.com/discuss/9929/a-java-solution-with-notes

``````public class Solution {
public void solveSudoku(char[][] board) {
if (board.length == 0) {
return;
}
solve(board);
}

public boolean solve(char[][] board) {
int m = board.length;

for (int i = 0; i < m; i++) {
for (int j = 0; j < m; j++) {
if (board[i][j] == '.') {
for (char c = '1'; c <= '9'; c++) {
if (isValid(board, i, j, c)) {
board[i][j] = c;
if (solve(board)) {
return true;
} else {
board[i][j] = '.';
}
}
}
return false;
}
}
}
return true;
}

public boolean isValid(char[][] board, int i, int j, char c) {
// check col
for (int row = 0; row < board.length; row++) {
if (board[row][j] == c) {
return false;
}
}
// check row
for (int col = 0; col < board.length; col++) {
if (board[i][col] == c) {
return false;
}
}
// check block

for (int row = (i/3)*3; row < (i/3)*3+3; row++) {
for (int col = (j/3)*3; col < (j/3)*3+3; col++) {
if (board[row][col] == c) {
return false;
}
}
}

return true;
}
}
``````