39. Combination Sum

public List<List<Integer>> combinationSum(int[] candidates, int target) {
List<List<Integer>> res = new ArrayList<List<Integer>>();
if(candidates == null || candidates.length == 0) {
return res;
}
Arrays.sort(candidates);
List<Integer> item = new ArrayList<Integer>();
helper(candidates, target, res, item, 0, 0);
return res;
}

private void helper(int[] candidates, int target, List<List<Integer>> res, List<Integer> item, int start, int curSum) {
if(start >= candidates.length || curSum > target) {
return;
}
if(curSum == target) {
if(!res.contains(item)) {
res.add(new ArrayList<Integer>(item));
}
return;
}
for(int i = start; i < candidates.length; i++){
item.add(candidates[i]);
helper(candidates, target, res, item, i, curSum + candidates[i]);
item.remove(item.size() - 1);
}
return;
}