Combination Sum

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]

 

Code:

?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

class Solution { public:     void findSum(vector<int> &S,int sum,int level,int &t,vector<int> &buf,vector<vector<int>> &res){         for(int i=level;i<S.size();i++){             buf.push_back(S[i]);             if(sum+S[i]==t)                 res.push_back(buf);             if(sum+S[i]<=t)                 findSum(S,sum+S[i],i,t,buf,res);             buf.pop_back();         }     }     vector<vector<int> > combinationSum(vector<int> &candidates, int target) {         vector<int> buf;         vector<vector<int>> res;         sort(candidates.begin(),candidates.end());         findSum(candidates,0,0,target,buf,res);         return res;     } };