# 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]&#x20;
>
> **Output:** true&#x20;
>
> **Explanation:** N = 10 is the double of M = 5,that is, 10 = 2 \* 5.

**Example 2:**

> **Input:** arr = \[7,1,14,11]&#x20;
>
> **Output:** true&#x20;
>
> **Explanation:** N = 14 is the double of M = 7,that is, 14 = 2 \* 7.

**Example 3:**

> **Input:** arr = \[3,1,7,11]&#x20;
>
> **Output:** false&#x20;
>
> **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**

```java
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;
}
```


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