Combination Sum

public class Solution {
    public ArrayList<ArrayList<Integer>> combinationSum(int[] candidates, int target) {
        // Start typing your Java solution below
        // DO NOT write main() function
        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
        int len = candidates.length, depth = 0;
        if(len == 0){
            return result;
        }
        ArrayList<Integer> output = new ArrayList<Integer>();
        int sum = 0;
        Arrays.sort(candidates);
        generate(result, output, sum, depth, len, target, candidates);
        return result;
    }
    
    public void generate(ArrayList<ArrayList<Integer>> result, ArrayList<Integer> output, int sum,
            int depth, int len, int target, int[] candidates){
            if(sum > target){
                return;
            }
            if(sum == target){
                ArrayList<Integer> tmp = new ArrayList<Integer>();
                tmp.addAll(output);
                result.add(tmp);
                return;
            }
            
            for(int i = depth; i < len; i++){
                sum += candidates[i];
                output.add(candidates[i]);
                generate(result, output, sum, i, len, target, candidates);
                sum -= output.get(output.size() - 1);
                output.remove(output.size() - 1);
            }
        }
}