Check If N and Its Double Exist

Description

Given an array arr of integers, check if there exists two integers N and M such that N is the double of M ( i.e. N = 2 * M).

More formally check if there exists 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: N = 10 is the double of M = 5,that is, 10 = 2 * 5.

Example 2:

Input: arr = [7,1,14,11]

Output: true

Explanation: N = 14 is the double of M = 7,that is, 14 = 2 * 7.

Example 3:

Input: arr = [3,1,7,11]

Output: false

Explanation: In this case does not exist N and M, such that N = 2 * M.

Constraints:

• 2 <= arr.length <= 500

• -10^3 <= arr[i] <= 10^3

Code

public boolean checkIfExist(int[] arr) {
    Map<Integer, Integer> map = new HashMap<>(arr.length);
    boolean exist = false;

    for (int item : arr) {
        map.compute(item, (k, v) -> {
            if (v == null) {
                return 1;
            }
            return v + 1;
        });
    }

    for (int value : arr) {
        Integer t = map.get(value * 2);
        if (t != null) {
            if (value == 0 && t != 2) {
                continue;
            }
            exist = true;
            break;
        }
    }
    return exist;
}