leecode40.组合总和||

 这题个人感觉很难，一开始按照正常的组合写法没有考虑到去重问题，根据以往写三四数之和的经验，对数组进行了排序，再进行去重逻辑的编写才得以通关，详细去重可以去看看代码随想录，甚至有使用到used数组讲解树枝和数层的去重

class Solution {
private:
    vector<vector<int>> result;
    vector<int> combination;

    void combinationSum2(vector<int>& candidates,int target,int count,int startIndex){
        if(count==target)
            result.push_back(combination);
        else{
            for(int i=startIndex;i<candidates.size()&&count<target;i++){
                //去重
                if(i>startIndex&&candidates[i]==candidates[i-1])
                    continue;

                combination.push_back(candidates[i]);
                combinationSum2(candidates,target,count+candidates[i],i+1);
                combination.pop_back();
            }
        }
    }
public:
    vector<vector<int>> combinationSum2(vector<int>& candidates, int target) {
        sort(candidates.begin(),candidates.end());
        combinationSum2(candidates,target,0,0);
        return result;
    }
};