There is an array of integers given. You have to find the lowest positive integer that does not exist in an array. The array can contain duplicates and negative numbers as well.

Write a function `solve`

that have the following parameter(s):

1.) *arr: an array of integer*

**Example**

Input:

`[3, 4, -1, 1]`

Output:

The function will return,

`2`

**Explanation**

In an array, there are `" -1, 1, 3, 4"`

given and the missing one is `2`

. So, the lowest positive integer that is missing is 2.

**Constraints**

• The size of the array will be greater than or equal to 1 and less than or equal to 800.

• An arr[i] will be greater than or equal to 0 and less than or equal to 1000.