219 Contains Duplicate II

class Solution {
public:
bool containsNearbyDuplicate(vector<int>& nums, int k) {
map<int, int> res;
int size = nums.size();
for(int i=0;i<size;++i)
{
if(res.find(nums[i])!=res.end())
{
if((i-res[nums[i]])<=k)
return true;
}
res[nums[i]] = i;
}
return false;
}
};