1346. Check If N and Its Double Exist

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

1. Use Brute Force:

//4 ms    9.9 MB
class Solution {
public:
    bool checkIfExist(vector<int>& arr) {
        for(int i = 0; i < arr.size()-1; i++){
            for(int j = i + 1; j < arr.size(); j++){
                if(arr[i] * 2 == arr[j]){
                    return true;
                } else if(arr[j] * 2 == arr[i]){
                    return true;
                }
            }
        }
        return false;
    }
};