Single Number

class Solution {
public:
    int singleNumber(vector<int>& nums) {
        std::unordered_map<int,int> count;
        int size=nums.size();
        for(int i=0;i<size;i++)
        {
            if(count.count(nums[i]))
                count[nums[i]]+=1;
            else
                count[nums[i]]=1;
        }
        for(auto it:count)
        {
            if(it.second==1)
                return it.first;
        }
        return 0;
    }
};