1346. Check If N and Its Double Exist

 

https://leetcode.com/problems/check-if-n-and-its-double-exist/

 

Source

class Solution {
public:
    bool checkIfExist(vector<int>& arr) {
        unordered_set<int> s;
        for (int n : arr) {
            if (s.count(2 * n) || (n % 2 == 0 && s.count(n / 2))) return true;
            s.insert(n);
        }
        return false;
    }
};