The ultimate guide to recursion interviews in JavaScript. Developed by FAANG engineers. Practice with real-world interview questions and get interview-ready in just a few hours.

If you’ve ever struggled with solving problems using recursion, or if you have to brush up your skills for an interview, this course is for you.

We'll start with the basics of what recursion is and why it’s important before diving into practicing solving actual questions. You’ll have access to detailed explanations and visualizations for each problem to help you along the way. 

By the time you have completed this course, you’ll be able to use all the concepts to solve complex real-world problems. We hope that through practicing recursion, you will be able to ace all recursion related questions in interviews at top tech companies.

Recursion for Coding Interviews in JavaScript

class Node {

	// constructor
	constructor(data) {
		this.data = data;
		this.next = null;
	}
}
module.exports =  Node;

import Node from './node.js'
class LinkedList {
	
	// constrictor
	constructor() {
		this.head = null;
	}
	
	// function for appending a new node in the linked list
	appendNode(newData) {
		newNode = new Node(newData);
		if (this.head == null) {
			this.head = newNode;
			return;
		}
		
		var last = this.head;
		while (last.next != null) {
			last = last.next;
		}
		last.next =  newNode;
	}
	
	//function for printing the linked list
	printList() {
		temp = this.head;
		while(temp != null) {
			console.log(temp.data);
			temp = temp.next;
		}
	}
}
module.exports =  LinkedList;


import LinkedList from './linkedList.js'

function length(testVariable, head) {
	// Base case
	if (head == null) {
		return 0;
	}
		
	// Recursive case
	else {
		return 1 + length(testVariable, head.next); 
	}
}

// Driver Code
var list = new LinkedList();
list.appendNode(4); 
list.appendNode(3); 
list.appendNode(11); 
list.appendNode(7); 
console.log(length(list, list.head))


### Explanation
Have a look at the function `length()` in `index.js` file.
 
The **base case (line number 5 to 7)** for this problem is when a linked list contains *no nodes*. In this case, we return $0$ as the length of that linked list.

For the **recursive case (line number 11)**, we move the head pointer to its next node, `head.next`, and call another instance of the same function recursively. When this child function returns, we add $1$ to the result.

Our solution is based on the following premise:
$length \: of \: a \: linked \: list = 1 + length \: of \: a \: linked \: list \: with \: head \:pointer \: moved \:one \: step\: ahead$.

Let's dry-run our code:


## Explanation
Have a look at the function `length()` in `index.js` file.
 
The **base case (line number 5 to 7)** for this problem is when a linked list contains *no nodes*. In this case, we return $0$ as the length of that linked list.

For the **recursive case (line number 11)**, we move the head pointer to its next node, `head.next`, and call another instance of the same function recursively. When this child function returns, we add $1$ to the result.

Our solution is based on the following premise:
$length \: of \: a \: linked \: list = 1 + length \: of \: a \: linked \: list \: with \: head \:pointer \: moved \:one \: step\: ahead$.

Let's dry-run our code:


This review provides a detailed analysis of the solution to find the length of a linked list.

Recursion Fundamentals

Iteration Vs Recursion

Recursion with Numbers

Recursion with Strings

Recursion with Arrays

Recursion with Data Structures

Conclusion

Solution Review: Length of a Linked List

Solution: Using Recursion

Explanation