### Check If N and Its Double Exist in an array - The Coding Shala

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# Check if N and its Double Exist in an array

In this post, we will learn how to check if N and its double exist in an array and will implement its solution in Java.

Given an array arr of integers, check if there exist 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 != jk
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.

## Check N and its double exist Solution

Approach:
We can check this using HashSet.
Check every number's double and if its divisible by two then check its half in the set.

Java Program:

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

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