39. Combination Sum(回溯)

Given a set of candidate numbers (candidates) (without duplicates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target.

The same repeated number may be chosen from candidates unlimited number of times.

Note:

All numbers (including target) will be positive integers.
The solution set must not contain duplicate combinations.

Example 1:

Input: candidates = [2,3,6,7], target = 7,
A solution set is:
[
  [7],
  [2,2,3]
]

Example 2:

Input: candidates = [2,3,5], target = 8,
A solution set is:
[
  [2,2,2,2],
  [2,3,3],
  [3,5]
]

 1 class Solution {
 2     private List<List<Integer>> res = new ArrayList<>();
 3     public List<List<Integer>> combinationSum(int[] candidates, int target) {
 4         List<Integer> temp = new ArrayList<Integer>();
 5         help(temp,candidates,0,0,target);
 6         return res;
 7     }
 8     private void help(List<Integer> temp,int[] nums,int index,int cursum,int target){
 9         if(cursum>target)
10             return;
11         if(cursum==target)
12             res.add(new ArrayList<Integer>(temp));
13         for(int i = index;i<nums.length;i++){
14             temp.add(nums[i]);
15             help(temp,nums,i,cursum+nums[i],target);
16             temp.remove(temp.size()-1);
17         }
18     }
19 }

2019.3.12

 1 class Solution {
 2 public:
 3     vector<vector<int>> finalres ;
 4     vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
 5         if(candidates.size()==0) return finalres;
 6         vector<int> curres;
 7         help(0,curres,candidates,0,target);
 8         return finalres;
 9         
10     }
11     void help(int cursum,vector<int>& curres,vector<int>& candidates,int index,int target){
12         if(cursum==target)
13             finalres.push_back(curres);
14         if(cursum>target)
15             return;
16         for(int i = index;i<candidates.size();i++){
17             curres.push_back(candidates[i]);
18             help(cursum,curres,candidates,i,target-candidates[i]);
19             curres.pop_back();
20 
21         }
22     }
23 };