Combination Sum

public class Solution {
    /**
     * @param candidates: A list of integers
     * @param target:An integer
     * @return: A list of lists of integers
     */
    public List<List<Integer>> combinationSum(int[] candidates, int target) {
        // write your code here
        List<List<Integer>> result = new ArrayList<List<Integer>>();
        if(candidates.length == 0 || candidates == null){
            return result;
        }
        List<Integer> list = new ArrayList<Integer>();
        Arrays.sort(candidates);
        combinationSumHelper(result, list, candidates, target, 0);
        return result;
    }
    
    private void combinationSumHelper(List<List<Integer>> result, 
                                      List<Integer> list,
                                      int[] candidates, 
                                      int target,
                                      int pos){
        if(target == 0){
            result.add(new ArrayList<Integer>(list));  
        }
        
        for(int i = pos; i < candidates.length; i++){
            if(candidates[i] > target){
                break;
            } 
            
            if( i > pos && candidates[i] == candidates[i-1]){
                continue;
            }
            
            list.add(candidates[i]);
            combinationSumHelper(result, list, candidates, target-candidates[i], i);
            list.remove(list.size() -1);
        }
    }
}