Leetcode 219 Contains Duplicate II STL

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