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

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);
        }
    }
}