LeetCode--Combination Sum

题目链接：

https://oj.leetcode.com/problems/combination-sum/

思路：

题目要求合并的答案需要升序排序。所以先排序，然后每次选一个，递归处理。

注意：每个元素可以多次，然后不能有重复的答案，所以碰到处理过的元素就不处理了。

class Solution {
public:
    vector<vector<int> >ans;
    vector<vector<int> > combinationSum(vector<int> &candidates, int target) {
        if(candidates.size() == 0)
            return ans;
        sort(candidates.begin(),candidates.end());
        deque<int> res;
        calSum(candidates,target,0,res);
        return ans;
    }
    void calSum(vector<int> &candidates,int target,int s,deque<int> &res)
    {
        if(target < 0)
            return;
        if(target == 0)
        {
            vector<int> restmp(res.begin(),res.end());
            ans.push_back(restmp);
            return;
        }
        int i;
        for(i = s ; i < candidates.size() ; ++i)
        {
            if(i > 0 && (candidates[i] == candidates[i-1]) )
                continue;
            res.push_back(candidates[i]);
            calSum(candidates,target-candidates[i],i,res);
            res.pop_back();
        }
        return;
    }
};