String Reversal Approaches in DSA Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the simplest way to reverse a string in Python using slicing?

Use slicing with a step of -1: reversed_string = original_string[::-1]. This creates a new string with characters in reverse order.

intermediate

How does the two-pointer approach reverse a string?

It uses two pointers: one at the start and one at the end of the string (or list). Swap characters at these pointers and move them towards the center until they meet.

beginner

Why can't strings be reversed in-place in Python?

Strings in Python are immutable, meaning they cannot be changed after creation. To reverse, you must create a new string or convert to a list first.

beginner

What is the time complexity of reversing a string using slicing or two-pointer approach?

Both approaches have a time complexity of O(n), where n is the length of the string, because each character is visited once.

intermediate

How can you reverse a string using a stack?

Push each character onto a stack, then pop characters off to build the reversed string. This uses the Last-In-First-Out property of stacks.

Which Python syntax reverses a string in one line?

A string[::-1]

B string.reverse()

C reversed(string)

D string.reverse

The slicing syntax string[::-1] returns a new string reversed. string.reverse() does not exist for strings.

Why can't you reverse a string in-place in Python?

A Python does not support reversal

B Strings are too long

C Strings are stored in reverse order

D Strings are immutable

Strings cannot be changed after creation in Python, so in-place reversal is not possible.

What data structure can help reverse a string by pushing and popping characters?

A Stack

B Queue

C Linked List

D Heap

A stack uses Last-In-First-Out order, which helps reverse the order of characters.

What is the time complexity of reversing a string of length n?

A O(n^2)

B O(1)

C O(n)

D O(log n)

Reversing requires visiting each character once, so it is O(n).

In the two-pointer approach, what do the pointers do?

A Move only forward swapping characters

B Swap characters from start and end moving inward

C Skip characters at odd positions

D Only swap characters at even positions

Two pointers start at opposite ends and swap characters while moving towards the center.

Explain three different ways to reverse a string in Python and their key differences.

Think about built-in features, manual swapping, and data structures.

Describe why strings in Python cannot be reversed in-place and how you can work around this limitation.

Focus on immutability and creating new strings.