Daily 3 questions (3) - check whether integers and their multiples exist

subject ：

Give you an array of integers  arr, Please check whether there are two integers  N and M, Satisfy  N  yes  M  Twice as many （ namely ,N = 2 * M）.

More formally , Check if there are two subscripts  i and j Satisfy ：

i != j
0 <= i, j < arr.length
arr[i] == 2 * arr[j]

Example 1：

Input ：arr = [10,2,5,3]
Output ：true
explain ：N = 10 yes M = 5 Twice as many , namely 10 = 2 * 5 .
Example 2：

Input ：arr = [7,1,14,11]
Output ：true
explain ：N = 14 yes M = 7 Twice as many , namely 14 = 2 * 7 .
Example 3：

Input ：arr = [3,1,7,11]
Output ：false
explain ： Does not exist in this case N and M Satisfy N = 2 * M .

Tips ：

2 <= arr.length <= 500
-10^3 <= arr[i] <= 10^3

Ideas ：

Store all the numbers in the hash table first , Then traverse all the numbers xx, Judge 2x2x Whether it is in the hash table .

java Code ：

class Solution {
     public boolean checkIfExist(int[] arr) {
        HashSet<Integer> set = new HashSet<>();
        for (int i : arr) {
            if (set.contains(2 * i) || (i % 2 == 0 && set.contains(i / 2)))
                return true;
            set.add(i);
        }
        return false;
    }
}