统计数组中只出现一次的数字

class Solution {
public:
    vector<int> findNumsAppearOnce(vector<int>& nums) {
        vector<int>ans;
        unordered_map<int,int>hash;
        for (int i=0;i<nums.size();i++)
            hash[nums[i]]++;
        for (int i=0;i<nums.size();i++)
        {
            if (hash[nums[i]]==1) ans.push_back(nums[i]);
        }
        return ans;
    }
};