SodukuSolver

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...

leetcode solution 





public class Solution {
    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 num = '1' ; num<='9' ; num++){
                   
                    if( isValid(board ,i,j,num)){
                board[i][j]=num;
                
                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 i , int j , char c){
        
        //check for col
        
        for(int row = 0 ; row < 9 ; row++){
            
            if( board[row][j] == c) {return false;}
            
        }
        
        //check for row
          for(int col = 0 ; col < 9 ; col++){
            
            if( board[i][col] ==c){ return false;}
            
        }
        //check for 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;
    }
}