Lintcode: k Sum II

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.

这道题同Combination Sum II

 1 public class Solution {

 2     /**

 3      * @param A: an integer array.

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

 5      * @param target: a integer

 6      * @return a list of lists of integer 

 7      */ 

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

 9         // write your code here

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

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

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

13         return res;

14     }

15     

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

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

18             if (remain == 0) {

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

20             }

21             return;

22         }

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

24             path.add(A[i]);

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

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

27         }

28     }

29 }