k Sum II

Given n unique integers, number k

Example

Given [1,2,3,4], k = 2, target = 5. Return:

[
  [1,4],
  [2,3]
]

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
     */ 

    ArrayList<ArrayList<Integer>> res=new ArrayList<ArrayList<Integer>>();
    public ArrayList<ArrayList<Integer>> kSumII(int[] A, int k, int target) {
        // write your code here

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

        if(A.length==0 || A==null || k>A.length || k<0) return res;

        kSum(A,0,k,target,list);

        return res;

    }

    public void kSum(int[] A,int begin,int k, int target,ArrayList<Integer> preList)
    {

        if (k == 0)
        {
            if (target == 0)
                res.add(new ArrayList<Integer>(preList));
            return;
        }

        for(int i=begin;i<A.length;i++)
        {
                preList.add(A[i]);
                kSum(A,i+1,k - 1,target-A[i],preList);
                preList.remove(preList.size()-1);
        }
    }
}