leetcode-1346-easy

Check if N and Its Double Exist

Given an array arr of integers, check if there exist two indices i and j such that :

i != j
0 <= i, j < arr.length
arr[i] == 2 * arr[j]
Example 1:

Input: arr = [10,2,5,3]
Output: true
Explanation: For i = 0 and j = 2, arr[i] == 10 == 2 * 5 == 2 * arr[j]
Example 2:

Input: arr = [3,1,7,11]
Output: false
Explanation: There is no i and j that satisfy the conditions.

Constraints:

2 <= arr.length <= 500
-103 <= arr[i] <= 103

思路一：用 set 判断，注意除法整除问题

    public static boolean checkIfExist(int[] arr) {
        Set<Integer> set = new HashSet<>();

        for (int i : arr) {
            if (set.contains(i * 2) || ((i & 1) == 0) && set.contains(i / 2)) {
                return true;
            }

            set.add(i);
        }

        return false;
    }