1346.Check-If-N-and-Its-Double-Exist.cpp

class Solution {
public:
    bool checkIfExist(vector<int>& arr) {
        unordered_set<int> st;
        for(int i = 0; i < arr.size(); ++i){
            if(st.find(2 * arr[i]) != st.end() || ((arr[i] % 2 == 0) && st.find(arr[i] / 2) != st.end())) return true;
            st.insert(arr[i]);
        }
        return false;
    }
};