Reverse Array #

Problem #

Given an array. Reverse the array in place.

Examples #

  • [1, 4, 3, 2, 6, 5] ➜ [5, 6, 2, 3, 4, 1]

  • [4, 5, 2] ➜ [2, 5, 4]

  • [1] ➜ [1]

Constraints #

  • 1 ≤ arr.size() ≤ 10⁵

  • 0 ≤ arr[i] ≤ 10⁵

Expected Complexities #

  • Time Complexity: O(n)O(n)

  • Auxiliary Space: O(1)O(1)

Solution #

Python
Numeric = int | float


def reverse_array_single_pointer(arr: list[Numeric]) -> list[Numeric]:
    for i in range(0, len(arr) // 2):
        arr[i], arr[-1 - i] = arr[-1 - i], arr[i]

    return arr


def reverse_array_two_pointers(arr: list[Numeric]) -> list[Numeric]:
    left_index: int = 0
    right_index: int = len(arr) - 1

    while left_index < right_index:
        arr[left_index], arr[right_index] = arr[right_index], arr[left_index]
        left_index += 1
        right_index -= 1

    return arr


print(reverse_array_single_pointer([1, 4, 3, 2, 6, 5]))
print(reverse_array_single_pointer([4, 5, 2]))
print(reverse_array_single_pointer([1]))