力扣-442题 数组中重复的数据（C++）- hash

题目链接：https://leetcode-cn.com/problems/find-all-duplicates-in-an-array/
题目如下：

class Solution {
public:
    vector findDuplicates(vector& nums) {
        vector res;
        unordered_map umap;

        for(auto e:nums){
            umap[e]++;
            if(umap[e]==2){
                res.push_back(e);
                umap.erase(e);
            }
        }

        return res;
    }
};