Mandatory Algorithms for Coding Interview

Basic algorithms that you must know if you want to crack your coding interview. In case you are starting to prepare for coding practice then make sure you learn all of these important algorightms. Get the source code for basic algorithms in JavaScript here

Binary Search in Sorted Array

**O(log(n) time

O(1) space**

See the Pen Binary Search Tree Implementation by Rupesh Tiwari (@rupeshtiwari) on CodePen.

Kadane’s Algorithm

See the Pen Kadane's Algorithm by Rupesh Tiwari (@rupeshtiwari) on CodePen.

Moore’s Voting Algorithm

See the Pen Moore's Voting Algorithm | Majority Sum | Array by Rupesh Tiwari (@rupeshtiwari) on CodePen.

Reverse Linked List

**O(n) time

O(1) space**

See the Pen Reverse Linked List Algorithm by Rupesh Tiwari (@rupeshtiwari) on CodePen.

Flyod’s Cycle Detection Algorithm

See the Pen Untitled by Rupesh Tiwari (@rupeshtiwari) on CodePen.

Sorting Algorithms

Merge sort

In Merge sort since I need 2 Aux arrays. And it requires more space to solve merge sorting problem. Therefore, I will prefer Linked List datastructure. Because, in linkedlist to store values, I do not need contigous memory slots. Hence optimizing memory usage.

**O(n log (n)) time

O(1) space**

See the Pen Merge Sort Algorithm by Rupesh Tiwari (@rupeshtiwari) on CodePen.

Quick Sort

**O(n log (n)) time

O( log (n) ) and wrost case O(n) space**

Quicksort is best fit for sorting Arrays since it is completely in-place sorting. No auxilary arrays are requried. So no need to store contigous memory slots on computer.

See the Pen Quick Sort In-place Implementation: Answer by Rupesh Tiwari (@rupeshtiwari) on CodePen.

Partition Logic

• All the element lesser than pivot are pushed to the left of the partition index (use swap)

Tree Traversal

Breadth-First Traversal(BFT)

Whenever tree is Sparse use BFT

**O(n) time

O(n) space**

See the Pen Breadth First Traversal | Binary Tree by Rupesh Tiwari (@rupeshtiwari) on CodePen.

Depth-First Traversal (DFT)

**O(n) time

O(n) space**

See the Pen Depth-First Traversal | Binary Tree by Rupesh Tiwari (@rupeshtiwari) on CodePen.

Binary Search Tree (BST)

See the Pen Binary Search Tree Implementation by Rupesh Tiwari (@rupeshtiwari) on CodePen.

Insert in Binary Search Tree (BST)

**O(Log(n)) time

Space O(1)**

For 1 insert operation, avg case is O(lgn) and worst case is O(n) For n insert operations, avg case is O(nlgn) and worst case is O(n^2)

Remove Node from BST

**O(log n) time

space O(1)**

Search in BST

O(log(n)) time | O(1)

Min Max and Height in BST

Heap implementation

In the interview no one will ask you to implement heap. This excercise is for your coding skills imporvement. In the interview, you can use array instead of heap and explain the concept.

See the Pen Heaps: Implement Heap by Rupesh Tiwari (@rupeshtiwari) on CodePen.

Insert node in the Heap

**O(log(n) time

O(1) space**

Revove root node from the Heap

**O(log(n) time

O(1) space**

Reference

• My Code School Youtube channel
• Source code of mandatory algorithms in JavaScript

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Rupesh Tiwari
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