LeetCode Single Number

Method I

class Solution {
public:
    int singleNumber(int A[], int n) {
        int mySum = 0, sum = 0;
        map<int, int>toolMap;
        for(int i = 0; i<n; i++)
        {
            sum+=A[i];
            toolMap.insert(pair<int, int>(A[i], 0));
        }
        for(map<int, int>::iterator iter = toolMap.begin(); iter!=toolMap.end();++iter)
        {
            mySum+= iter->first;
        }
        int re = mySum*2 - sum; 
        
        return re;
    }
};