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] 

       先排序，然后对于每个元素，DFS遍历后续元素看和是否等于7。>7返回，<7继续，==7保存并返回。

       由于集合set里面没有重复元素，所以不用考虑有重复的组合。

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