Combination Sum [LeetCode]

Problem Description: http://oj.leetcode.com/problems/combination-sum/　　　　

Basic idea: It seems complicate at first. But once I got the recursive idea, the solution was neat. This code could be not efficient. I will rewrite with dynamic programming next time.

class Solution {
public:
    vector<vector<int> > combinationSum(vector<int> &candidates, int target) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        std::sort(candidates.begin(), candidates.end());
        vector<vector<int> > combinations;
        for(int i = 0; i < candidates.size(); i ++) {
            if(candidates[i] > target)
                break;
            if(candidates[i] == target) {
                vector<int> combination;
                combination.push_back(candidates[i]);
                combinations.push_back(combination);
            }else{
                if(i == 0 && target % candidates[i] != 0)
                    continue;
                if(i == 0 && target % candidates[i] == 0){
                    vector<int> combination(target / candidates[i], candidates[i]);
                    combinations.push_back(combination);
                    continue;
                }
                vector<int> sub_candidates(candidates.begin(), candidates.begin() + i + 1);
                vector<vector<int> > rests =  combinationSum(sub_candidates, target - candidates[i]);
                for(auto item: rests){
                    item.push_back(candidates[i]);
                    combinations.push_back(item);
                }
            }
        }
        return combinations;
    }
};