LeetCode 39 - Combination Sum

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] 

My Code

class Solution {public:    void doCombinationSum(vector<vector<int> >& sets, vector<int>& set, vector<int>& candidates, int target, int idx)    {        if (0 == target)        {            sets.push_back(set);            return;        }        for (int i = idx; i < candidates.size() && candidates[i] <= target; i++)        {            set.push_back(candidates[i]);            doCombinationSum(sets, set, candidates, target - candidates[i], i);            set.pop_back();        }    }    vector<vector<int> > combinationSum(vector<int>& candidates, int target) {        vector<int> set;        vector<vector<int> > sets;        sort(candidates.begin(), candidates.end());        doCombinationSum(sets, set, candidates, target, 0);        return sets;    }};

Runtime: 16 ms