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

Recall & Review

beginner

What is recursion in the context of arrays and strings?

Recursion is a way where a function calls itself to solve smaller parts of a problem, like breaking an array or string into smaller pieces until it reaches a simple case.

beginner

How do you identify the base case in recursion on arrays or strings?

The base case is the simplest part where the function stops calling itself, often when the array or string is empty or has one element.

intermediate

Explain how recursion can be used to reverse a string.

To reverse a string recursively, take the first character, call the function on the rest of the string, then add the first character at the end of the result.

beginner

What happens if a recursive function on an array does not have a proper base case?

Without a proper base case, the function will keep calling itself forever, causing a stack overflow error.

beginner

Show a simple recursive approach to find the sum of elements in an array.

Sum the first element and then call the function on the rest of the array until the array is empty (base case).

What is the base case when recursively processing a string?

A When the string is longer than the array

B When the string has more than 10 characters

C When the string contains only vowels

D When the string is empty or has one character

The base case is when the string is empty or has one character, which stops further recursion.

In recursion on arrays, what does the function usually do after processing the first element?

A Calls itself with the rest of the array

B Returns the first element immediately

C Processes the last element next

D Stops recursion

After processing the first element, the function calls itself with the rest of the array to continue the process.

What error occurs if recursion has no base case?

A Syntax error

B Stack overflow

C Type error

D Memory leak

Without a base case, recursion never stops, causing a stack overflow error.

Which of these is a good example of a base case for recursion on an array?

A Array is sorted

B Array length is greater than 5

C Array length is zero

D Array contains only even numbers

The base case is usually when the array length is zero, meaning no more elements to process.

How can recursion help in reversing an array?

A By swapping first and last elements and calling itself on the middle part

B By sorting the array

C By adding elements to the end

D By removing duplicates

Recursion can reverse an array by swapping the first and last elements and then calling itself on the smaller middle part.

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

Think about how to break the array into smaller parts and when to stop.

Describe the steps to reverse a string using recursion.

Focus on how the function processes one character and calls itself on the rest.