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

Recall & Review

beginner

What is the simplest way to reverse a string in C using a loop?

Use two pointers: one at the start and one at the end of the string. Swap characters at these pointers and move them towards the center until they meet or cross.

intermediate

How does recursion help in reversing a string?

Recursion reverses a string by swapping the first and last characters and then calling itself on the substring excluding these characters until the base case (empty or single character) is reached.

beginner

What is the role of the null character '\0' in C strings during reversal?

The null character marks the end of the string. It should not be moved or swapped during reversal to avoid corrupting the string termination.

beginner

Why is it important to handle string length correctly before reversal?

Knowing the string length helps set the correct end pointer for swapping characters. Incorrect length can cause out-of-bound errors or incomplete reversal.

intermediate

Can you reverse a string in C without using extra memory? How?

Yes, by swapping characters in place using two pointers moving from start and end towards the center, no extra memory is needed.

Which method uses two pointers to reverse a string in C?

A Using string concatenation

B Using a temporary array to store reversed string

C Using recursion without swapping

D Swapping characters from start and end moving inward

The two-pointer method swaps characters from the start and end moving inward until the string is reversed.

What is the base case in recursive string reversal?

A When the string is longer than 10 characters

B When the string contains only vowels

C When the string length is zero or one

D When the string contains spaces

The recursion stops when the string is empty or has a single character, as it is already reversed.

Why should the null character '\0' not be swapped during reversal?

A It marks the end of the string and swapping it breaks the string

B It is a visible character

C It is a space character

D It is a number

The null character marks the string end; moving it corrupts the string termination.

Which function is commonly used to find string length before reversal in C?

A strlen()

B strrev()

C strcpy()

D strcmp()

strlen() returns the length of the string, needed to set pointers for reversal.

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

A O(n^2)

B O(n)

C O(log n)

D O(1)

Each character is swapped once, so the time complexity is linear, O(n).

Explain how to reverse a string in C using the two-pointer approach.

Think about swapping characters from both ends moving towards the center.

Describe the recursive method to reverse a string and its base case.

Recursion breaks the problem into smaller parts until a simple case is reached.