Given n unique integers, number k (1<=k<=n)  and target. Find all possible k integers where their sum is target.

Example

Given [1,2,3,4], k=2, target=5, [1,4] and [2,3] are possible solutions.

 public class Solution {

     /**

      * @param A: an integer array.

      * @param k: a positive integer (k <= length(A))

      * @param target: a integer

      * @return a list of lists of integer

      */

     public ArrayList<ArrayList<Integer>> kSumII(int A[], int k, int target) {

         // write your code here

         ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();

         ArrayList<Integer> path = new ArrayList<Integer>();

         helper(res, path, A, k, target, 0);

         return res;

     }

     public void helper(ArrayList<ArrayList<Integer>> res, ArrayList<Integer> path, int[] A, int k, int remain, int index) {

         if (path.size() == k) {

             if (remain == 0) {

                 res.add(new ArrayList<Integer>(path));

             }

             return;

         }

         for (int i=index; i<A.length; i++) {

             path.add(A[i]);

             helper(res, path, A, k, remain-A[i], i+1);

             path.remove(path.size()-1);

         }

     }

 }