219. Contains Duplicate II

class Solution {public:    bool containsNearbyDuplicate(vector<int>& nums, int k) {        set<int> pot;        for(int i = 0; i < nums.size(); ++i){            if(i > k)                pot.erase(nums[i-k-1]);            if(!pot.insert(nums[i]).second) return true;        }        return false;    }};