Combination Sum.java

Given a set of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.

The same repeated number may be chosen from C unlimited number of times.

Note:

All numbers (including target) will be positive integers.
Elements in a combination (a1, a2, ? , ak) must be in non-descending order. (ie, a1 ? a2 ? ? ? ak).
The solution set must not contain duplicate combinations.
For example, given candidate set 2,3,6,7 and target 7, 
A solution set is: 
[7] 
[2, 2, 3] 

public class Solution {
    public ArrayList<ArrayList<Integer>> combinationSum(int[] candidates, int target) {
	ArrayList<ArrayList<Integer>> ret = new ArrayList<ArrayList<Integer>>();
	ArrayList<Integer> solution = new ArrayList<Integer>();
	Arrays.sort(candidates);
	combinationSum(candidates, 0, 0, target, ret, solution);
	return ret;
    }

    private void combinationSum(int[] candidates, int start, int sum, int target, ArrayList<ArrayList<Integer>> ret, ArrayList<Integer> solution) {
    if (sum == target) {
	ret.add(new ArrayList<Integer>(solution));
	return;
    }
    if (start > candidates.length - 1) return;
	int times = 0;
	while(true) {
	    if (sum > target) {
	        for (int h = 0; h < times; h++) {
		    solution.remove(solution.size() - 1);
		}
		break;
	    }
	    combinationSum(candidates, start + 1, sum, target, ret, solution);
	    sum += candidates[start];
	    solution.add(candidates[start]);
	    times++;
	}
    }
}