[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] 

DFS!

class Solution {
public:
    void findNext(vector<vector<int> > &res, vector<int> &candidates, vector<int> v, int sum, int target, int idx) {
        if (sum > target || idx >= candidates.size()) {
            return;
        }
        if (sum == target) {
            res.push_back(v);
            return;
        }
        v.push_back(candidates[idx]);
        findNext(res, candidates, v, sum + candidates[idx], target, idx);
        v.pop_back();
        findNext(res, candidates, v, sum, target, idx + 1);
    }
    
    vector<vector<int> > combinationSum(vector<int> &candidates, int target) {
        vector<vector<int> > res;
        sort(candidates.begin(), candidates.end());
        vector<int> v;
        findNext(res, candidates, v, 0, target, 0);
        return res;
    }
};