Given an array of integers and a target integer, return the *indices* of the FIRST two numbers which add up to the target.

Assume the same element may not be used twice.

#### Example

```
twoSum([1,2,3], 4);
//returns [0, 2] because 1 + 3 equals 4
```

Given an array of integers and a target integer, return the *indices* of the FIRST two numbers which add up to the target.

Assume the same element may not be used twice.

```
twoSum([1,2,3], 4);
//returns [0, 2] because 1 + 3 equals 4
```