Recursion on Arrays and Strings in DSA C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is recursion in the context of arrays and strings?

Recursion is a method where a function calls itself to solve smaller parts of a problem, like processing elements of an array or characters of a string one by one until a base case is reached.

beginner

What is the base case in a recursive function working on an array?

The base case is the condition that stops the recursion, often when the array index reaches the end or when the size of the array segment to process is zero.

intermediate

How does recursion help in reversing a string?

Recursion reverses a string by swapping characters from the start and end, then calling itself on the smaller substring inside, until the base case of one or zero characters is reached.

beginner

Explain how to find the sum of elements in an array using recursion.

To find the sum recursively, add the first element to the sum of the rest of the array found by a recursive call, stopping when the array is empty (base case).

beginner

What happens if a recursive function on arrays or strings does not have a proper base case?

Without a proper base case, the recursion will continue indefinitely, causing a stack overflow error and crashing the program.

What is the base case when recursively printing all elements of an array?

A When the index reaches the array length

B When the array is empty

C When the first element is zero

D When the last element is reached

The base case is when the index reaches the array length, meaning no more elements to print.

Which of these is a correct recursive step to reverse a string?

A Reverse the string without changing characters

B Swap first and second characters only

C Swap characters randomly

D Swap first and last characters, then reverse the substring inside

The recursive step swaps the first and last characters, then calls itself on the substring inside.

What does a recursive function typically do after processing one element of an array?

A Processes the entire array again

B Returns immediately

C Calls itself with the next element

D Stops execution

After processing one element, the function calls itself with the next element to continue recursion.

Why is a base case important in recursion?

A To stop the recursion and avoid infinite calls

B To start the recursion

C To increase the recursion depth

D To print the array

The base case stops recursion to prevent infinite calls and stack overflow.

How can recursion be used to count the number of characters in a string?

A Count all characters at once

B Count 1 for the first character plus count of the rest recursively

C Use a loop instead

D Count only vowels

Recursion counts 1 for the current character plus the count from the rest of the string.

Describe how recursion works on arrays with an example of summing elements.

Think about stopping condition and how each call handles one element.

Explain the steps to reverse a string using recursion.

Focus on how the string is reduced each time.