Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

Write a function `solve`

that have the following parameter(s):

1.) *arr = array of integers*

**Example**

Input:

`[100, 4, 200, 1, 3, 2]`

Output:

`4`

**Explanation**

An array `[100, 4, 200, 1, 3, 2]`

is given. The longest consecutive element sequence is [1, 2, 3, 4]. So, it will return `4`

.

**Constraints**

• The length of an array should greater than 0 or less than 800.

• The elements in the array should be greater than 0 and less than 1000.