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56 | public class Solution {
public void solveSudoku(char[][] board) {
dfs(board, 0, 0);
}
private boolean dfs(char[][] board, int row, int col){
if (row >= 9) return true;
int nextCol = (col+1)%9;
int nextRow = row+(col+1)/9;
if (board[row][col] != '.') return dfs(board, nextRow, nextCol);
else{
for (int i = 0; i < 9; i++){
board[row][col] = (char)(i+'1');
if (isValid(board, row, col) && dfs(board, nextRow, nextCol)) return true;
board[row][col] = '.';
}
}
return false;
}
private boolean isValid(char[][] board, int row, int col){
boolean lookup[] = new boolean[9];
//check row
for (int i = 0; i < 9; i ++){
if (board[row][i] != '.'){
int index = board[row][i] - '0' -1;
if (lookup[index]) return false;
lookup[index] = true;
}
}
//check column
lookup = new boolean[9];
for (int i = 0; i < 9; i++){
if (board[i][col] != '.'){
int index = board[i][col] - '0' - 1;
if(lookup[index]) return false;
lookup[index] = true;
}
}
//check box
int startingRow = (row/3)*3;
int startingCol = (col/3)*3;
lookup = new boolean[9];
for (int i = startingRow; i < startingRow+3; i++){
for (int j = startingCol; j < startingCol+3; j++){
if (board[i][j] != '.'){
int index = board[i][j] - '0' - 1;
if (lookup[index]) return false;
lookup[index] = true;
}
}
}
return true;
}
}
|
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