Contains Duplicate

class Solution {
public:
bool containsDuplicate(vector<int>& nums) {
map<int,int> mymap;
int size=nums.size();
for(int i=0;i<size;i++)
{
if(mymap.find(nums[i])==mymap.end())
{
mymap.insert(pair<int,int>(nums[i],1));

}
else
{
return true;
}
}

return false;
}
};