#### Find the First Duplicate

You are given an array of integers containing some duplicates as an argument. Return the first element in the array that is duplicated twice.

### Requirements

- Must return an integer
- Must also handle negative integers
- Must be able to handle cases with multiple duplicate elements

#### Example #1

```
solve([6, 2, 5, 1, 0, 12, 2])
> 2
```

#### Example #2

```
solve([-6, 1, 5, -6, 0, -2, 3])
> -6
```

#### Example #3

```
solve([3, 1, 5, 1, 0, -2, 3, 5])
> 1
```

The number three appears twice, but both instances of the number one appear before both instances of three, so return one.