//经典回溯法
class Solution {
public:
vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
vector<vector<int>> res;
sort(candidates.begin(),candidates.end());
vector<int> add;
DFS(candidates,target,0,add,res);
return res;
}
void DFS(vector<int>& candidates, int target,int start,vector<int>& add,vector<vector<int>>& res){
if(target < 0)return;
else if(target == 0){res.push_back(add);}
else{
for(int i=start;i < candidates.size();i++){
add.push_back(candidates[i]);
DFS(candidates,target-candidates[i],i,add,res);
add.pop_back();
}
}
}
};