[LeetCode] 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] 

class Solution {
public:
    vector<vector<int> > res;
    vector<int> v;
    vector<vector<int> > combinationSum(vector<int> &candidates, int target) {
        sort(candidates.begin(),candidates.end());
        generate(candidates,0,0,target);
        return res;
    }
    void generate(vector<int> cand,int sum,int start,int target){
        if(sum == target){
            res.push_back(v);
            return;
        }
        for(int i = start;i < cand.size();i ++){
            v.push_back(cand[i]);
            sum += cand[i];
            if(sum > target){
                v.pop_back();
                break;
            }
            generate(cand,sum,i,target);
            v.pop_back();
            sum -= cand[i];
        }
    }
};