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]
]

 class Solution {
     private List<List<Integer>> res = new ArrayList<>();
     public List<List<Integer>> combinationSum(int[] candidates, int target) {
         List<Integer> temp = new ArrayList<Integer>();
         help(temp,candidates,0,0,target);
         return res;
     }
     private void help(List<Integer> temp,int[] nums,int index,int cursum,int target){
         if(cursum>target)
             return;
         if(cursum==target)
             res.add(new ArrayList<Integer>(temp));
         for(int i = index;i<nums.length;i++){
             temp.add(nums[i]);
             help(temp,nums,i,cursum+nums[i],target);
             temp.remove(temp.size()-1);
         }
     }
 }

2019.3.12

 class Solution {
 public:
     vector<vector<int>> finalres ;
     vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
         if(candidates.size()==) return finalres;
         vector<int> curres;
         help(,curres,candidates,,target);
         return finalres;

     }
     void help(int cursum,vector<int>& curres,vector<int>& candidates,int index,int target){
         if(cursum==target)
             finalres.push_back(curres);
         if(cursum>target)
             return;
         for(int i = index;i<candidates.size();i++){
             curres.push_back(candidates[i]);
             help(cursum,curres,candidates,i,target-candidates[i]);
             curres.pop_back();

         }
     }
 };