In this HackerRank Ruby Array - Index, Part 1 problem-solution Array collections offer various ways to access their elements. The positions are 0 indexed. Objects of the array can be accessed using the [] method which may take various arguments, as explained below.

arr = [9, 5, 1, 2, 3, 4, 0, -1]

A number which is the position of an element

>>arr

=> 3

or

>>arr.at(4)

=> 3

A range indicating the start and the end position

>>arr[1..3] # .. indicates both indices are inclusive.

=> [5,1,2]

>>arr[1...3] # ... indicates the last index is excluded.

=> [5,1]

Start index and the length of the range

>>arr[1,4]

=> [5, 1, 2, 3]

## Problem solution.

```def element_at(arr, index)
arr[index]
end

def inclusive_range(arr, start_pos, end_pos)
arr[start_pos..end_pos]
end

def non_inclusive_range(arr, start_pos, end_pos)
arr[start_pos...end_pos]
end

def start_and_length(arr, start_pos, length)
arr[start_pos,length]
end
```

## Second solution.

```def element_at(arr, index)
# return the element of the Array variable `arr` at the position `index`
# arr.at(index) # or
arr[index]
end

def inclusive_range(arr, start_pos, end_pos)
# return the elements of the Array variable `arr` between the start_pos and end_pos (both inclusive)
arr[start_pos,(end_pos-start_pos+1)]
end

def non_inclusive_range(arr, start_pos, end_pos)
# return the elements of the Array variable `arr`, start_pos inclusive and end_pos exclusive
arr[start_pos,end_pos-start_pos]
end

def start_and_length(arr, start_pos, length)
# return `length` elements of the Array variable `arr` starting from `start_pos`
arr[start_pos,length]
end
```