Reverse an Array

Problem

Given an array of elements, reverse the array in-place.

This means you should modify the original array without using extra space for another array.

Implement multiple approaches:

1. Two-pointer swap (optimal in-place)
2. Using built-in reverse
3. Stack-based approach

After reversing:

• First element becomes last
• Second element becomes second-to-last
• And so on...

Constraints

• 0 ≤ array length ≤ 10^5
• Array elements can be any type (integers, strings, etc.)
• Must modify array in-place with O(1) extra space

Examples

Example 1

Input:

arr = [1, 2, 3, 4, 5]

Output:

[5, 4, 3, 2, 1]

Explanation: Each element swaps with its mirror position

Example 2

Input:

arr = ["a", "b", "c", "d"]

Output:

["d", "c", "b", "a"]

Explanation: Works with any element type

Example 3

Input:

arr = [1]

Output:

[1]

Explanation: Single element array remains unchanged

Example 4

Input:

arr = []

Output:

[]

Explanation: Empty array remains empty

Function Signature

def reverse_array(arr: list) -> None:
    """
    Reverse the array in-place.

    Args:
        arr: The array to reverse (modified in-place)

    Returns:
        None (array is modified in-place)
    """
    pass

Estimated Time

10-15 minutes

Tags

two-pointers array easy fundamental interview