[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> > combinationSum(vector<int> &candidates, int target) {
        vector<vector<int>> res;
        if(candidates.empty())   return res;
        sort(candidates.begin(), candidates.end());
        vector<int> path;
        dfs(res, path, candidates, target, 0);
        return res;
    }
    void dfs(vector<vector<int>> &res, vector<int> &path, vector<int> &candidates, int target, int idx)
    {
        if(target == 0)
        {
            res.push_back(path);
            return;
        }
        if(idx == candidates.size() || candidates[idx] > target)
            return;
        for(int i = target / candidates[idx]; i >= 0; i--)
            path.push_back(candidates[idx]);
        for(int i = target / candidates[idx]; i >= 0; i--)
        {
            path.pop_back();
            dfs(res, path, candidates, target - i * candidates[idx], idx + 1);
        }
    }
};