[Leetcode][Backtracking] N-Queens II [Sanpchat]

1. What
http://codingweihung.blogspot.com/2015/08/leetcodebacktracking-n-queens-sanpchat.html
2. How
http://codingweihung.blogspot.com/2015/08/leetcodebacktracking-n-queens-sanpchat.html

NOTE: return total number of distinct solution 

What is distinct solution? 

how to represent a solution?  a String[], so distinct means different String[]

hashSet to store string array ?  to much hassle

hashSet to store int array which is columnWithQueenForRow

public class Solution
{
   // NOTE: can also declare a global variable int res, initialize in totalNQueens() and increment in helper()
   public int totalNQueens(int n)
   {
         int[] res = {0};
        /*validate the input */
        if ( n <= 0)
        {
            return res[0];
        }
        int[] columnWithQueenForRow = new int[n];
        helper(n, 0, columnWithQueenForRow, res);
   }
   
   /*recursive function to go over column by column*/
   private void helper (int size, int row , int[] ColumnWithQueenForRow, int[] res)
   {
       if ( row == n )
       {  
           /*NOTE: won;t have duplicate solution since start from different column*/
           res[0]+=1;
           return;
       }
       for (int j = 0 ; j < n ;j++)
       {
             columnWithQueenForRow[row] = j;
             if ( check(row, columnWithQueenForRow) )
             {
                   helper( n, row+1, columnWithQueenForRow, );
             }
       }
   }
   
   /* check valid move*/
   private boolean check (int row, int[] columnWithQueenForRow)
   {
       for ( int i = 0 ; i < row; i++)
       {
              if ( columnWithQueenForRow[row] == columnWithQueenForRow[i] || Math.abs( columnWithQueenForRow[row] - columnWithQueenForRow[i] ) == (row - i) ) 
              {
                    return false;
              }
       }
       return true;
   }
}