1539.Kth-Missing-Positive-Number_v1.cpp

class Solution {
public:
    int findKthPositive(vector<int>& arr, int k) 
    {
        unordered_set<int>Set(arr.begin(), arr.end());
        int count = 0;
        for (int i=1; i<=arr.back()+1000; i++)
        {
            if (Set.find(i)==Set.end())
                count+=1;
            if (count==k)
                return i;
        }
        return -1;
    }
};