leetcode JAVA Combination Sum 难度系数3 3.13

Question：

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>> results = new ArrayList<ArrayList<Integer>>();if (candidates.length == 0) {return results;}Arrays.sort(candidates);ArrayList<Integer> result = new ArrayList<Integer>();dfs(results, candidates, target, result, 0, 0);return results;}private void dfs(ArrayList<ArrayList<Integer>> results, int[] candidates,int target, ArrayList<Integer> result, int step, int sum) {if (sum == target) {if (!results.contains(result)) {results.add(new ArrayList<Integer>(result));}return;}if (sum > target) {return;}for (int i = step; i < candidates.length; i++) {result.add(candidates[i]);dfs(results, candidates, target, result, i, sum + candidates[i]);result.remove(result.size() - 1);}return;}}