cs

public ArrayList<ArrayList<Integer>> combinationSum(int[] candidates, int target) {
		 ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
		 if(candidates == null || candidates.length == 0) return result;
		 Arrays.sort(candidates); 
		 this.comSumHelper(candidates, target, 0, result, new ArrayList<Integer>(), 0);
		 return result;
	    }
	 public void comSumHelper(int[] candidates, int target, int start, ArrayList<ArrayList<Integer>> result, 
			 ArrayList<Integer> curSolution, int curSum ) {
		 if(curSum == target) {
			 //System.out.print("Sol!");
			 result.add(new ArrayList<Integer>(curSolution));
			 return;
		 }
		 if(curSum < target) {
			 for(int i = start; i< candidates.length; i++) { // Error: use i = start, not from beginning can elimate duplicate sol
				 curSum += candidates[i];
				 curSolution.add(candidates[i]);
				 
				 comSumHelper(candidates, target, i, result, curSolution, curSum);
				 curSum -= candidates[i];
				 curSolution.remove(curSolution.size()-1);
			 }
		 }
		 
		 return;
	 }