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@anil477
Created January 30, 2022 08:48
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37. Sudoku Solver
public class Solution {
// 37. Sudoku Solver
// https://leetcode.com/problems/sudoku-solver/
public void solveSudoku(char[][] board) {
if(board == null || board.length == 0)
return;
solve(board);
}
public 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++){ //trial. Try 1 through 9
if(isValid(board, i, j, c)){
board[i][j] = c; //Put c for this cell
if(solve(board))
return true; //If it's the solution return true
else
board[i][j] = '.'; //Otherwise go back
}
}
return false;
}
}
}
return true;
}
private boolean isValid(char[][] board, int row, int col, char c){
int regionRow = 3 * (row / 3); //region start row
int regionCol = 3 * (col / 3); //region start col
// System.out.println("row: "+ row + " col: " + col + " regionRow: " + regionRow+ " regionCol: " + regionCol);
for (int i = 0; i < 9; i++) {
if (board[i][col] == c) return false; //check row
if (board[row][i] == c) return false; //check column
// System.out.println("row: "+ (regionRow + i / 3) + " col: " + (regionCol + i % 3));
if (board[regionRow + i / 3][regionCol + i % 3] == c) return false; //check 3*3 block
}
return true;
}
}
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