[LeetCode] N-Queens

Follow up for N-Queens problem.
Now, instead outputting board configurations, return the total number of distinct solutions.





解题思路：问题，每步的solution都与前面的solution相关。要满足，当前的位置i没有被前面使用过并且 |x-y| != |x0 -y0|

Java Code:

 public int totalNQueens(int n) {
          
         ArrayList solution = new ArrayList ();
           
         return totalNq(solution, 0, n);     
    }
    
    public int totalNq(ArrayList orders, int level, int n){
           int total = 0;
           
           if(level == n) {
               return 1;
           }else{
               for(int col = 0; col < n; col++){  
                   
                   if(!orders.contains(col)){
                       int j = 0;
                       while(j < level && Math.abs(j - level) != Math.abs(orders.get(j) - col) ){              
                           j++;
                       }
                       
                       if( j == level){
                           orders.add(level, col);
                           total +=totalNq(orders, level + 1,n); 
                           orders.remove(level);
                       }
                   }
               }
           } 
           
           return total;
    }