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_37.java
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_37.java
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package com.fishercoder.solutions;
public class _37 {
public static class Solution1 {
public void solveSudoku(char[][] board) {
if (board == null || board.length == 0) {
return;
}
solve(board);
}
private boolean solve(char[][] board) {
for (int i = 0; i < board.length; i++) {
for (int j = 0; j < board[0].length; j++) {
if (board[i][j] == '.') {
for (char c = '1'; c <= '9'; c++) {
//try 1 to 9
if (isValid(board, i, j, c)) {
board[i][j] = c;
if (solve(board)) {
return true;
} else {
board[i][j] = '.';//recover it to be '.'
}
}
}
return false;
}
}
}
return true;
}
private boolean isValid(char[][] board, int row, int col, char c) {
for (int i = 0; i < 9; i++) {
if (board[i][col] != '.' && board[i][col] == c) {
return false;//check row
}
if (board[row][i] != '.' && board[row][i] == c) {
return false;//check column
}
if (board[3 * (row / 3) + i / 3][3 * (col / 3) + i % 3] != '.' && board[3 * (row / 3) + i / 3][3 * (col / 3) + i % 3] == c) {
return false; //check 3*3 block
}
}
return true;
}
}
}