[Leetcode] Combination Sum

class Solution {
public:
    vector<vector<int> > combinationSum(vector<int> &candidates, int target) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<vector<int> > res;
        vector<int> cache;
        sort(candidates.begin(), candidates.end());
        calculate(cache, 0, candidates, res, target);
        
        return res;
    }
    
    void calculate(vector<int> cache, int curIdx, vector<int>& candidates, vector<vector<int> >& res, int target)
    {
        if (curIdx >= candidates.size()) return;
        
        int i = 0;
        while (target - candidates[curIdx] * i >= 0)
        {
            for (int j = 0; j < i; ++j) 
            {
                cache.push_back(candidates[curIdx]);                
            }
            
            if (target - candidates[curIdx] * i == 0)
            {
                res.push_back(cache);
                break;
            }
                
            calculate(cache, curIdx + 1, candidates, res, target - candidates[curIdx] * i);
            
            for (int j = 0; j < i; ++j) 
            {
                cache.pop_back();                
            }
            
            ++i;
        }
    }
    
};