Venkatesh Thallam - Let's Talk Algorithms

How I built Stonks News

Everyone around me was trading meme stocks and most of them seem to be making reasonable profits. My obvious reaction was how do you guys come across these meme stocks before they take off? Most mention Reddit and the sub-reddit r/wallstreetbets in specific.

golang

2D Array Initialization in Golang

A two dimensional array in Go require you to explicitly allocate the space for the whole array. If you want a 2-D array with 4 rows and 5 columns of integer type, below is the sample code. arr := make([][]int, 4) for i := range

Analytics

Analysis of 2018 Hacker News "Who is Hiring" Job Posts

Image showing all the locations from the Hacker News Who is Hiring Job PostsIf you are an avid Hacker News user, you would know that there's a hiring comment thread during the start of every month called, Who is Hiring. Hundreds of companies from

Leetcode

Leetcode Premium vs Lintcode VIP

Leetcode, Lintcode, Hackerrank, Hackerearth and Interviewbit are some of the leading preparation platforms. Of all these, Leetcode is the most famous one because of its vast collection of questions and a company focussed preparation style.

Leetcode Medium

Longest Palindromic Substring Java

Problem Statement Given a string, Find the longest palindromic substring. Solution Explanation Understanding the question here is very simple, given a string RENTNOW, the substring NTN is a palindrome of length 3, and that would be the result. Brute Force Before we think of

Leetcode Easy

Balanced Parentheses Validation - Java

Problem Statement Given an string or expression which only consists of characters like (, ), [, ], {, } . Validate if the string has balanced parentheses. A string has balanced parentheses, if every open bracket has an associated closed one and they exist in the right order. Solution Explanation As

Frequently Asked Questions

Calculate the Hamming Distance between two Integers

Problem Statement Given two integers, calculate the hamming distance between them. Solution Explanation Hamming Distance between integers is defined as the number of indexes where the two bits differ. For example, given integers x = 2 and y=5, the hamming distance between them is,

Data Structures

Doubly Linked List Implementation Java

LinkedList is a linear data structure which allows to insert and remove elements at the front and rear in constant time. LinkedLists are typically of two types, Single LinkedList Each node has a reference to the next node. Doubly LinkedList Each node has a

Data Structures

Introduction to Queue and Implementation using Linked List

Queue is a linear datastructure that stores elements with first in first out(FIFO) ordering. That is, the element which gets added to the queue leaves before all the elements added after it. The most typical example is a real world queue, where you

Data Structures

Stack Implementation using Single LinkedList Java

Stack is one of the most used data structures in computer science. It is a linear data structure which supports ordering of elements in Last In First Out order(LIFO). The very typical real world example is a stack of plates, where new plates

Array

Trapping Rain Water Solution Java

Problem Statement Given an a list of n integers which are non negative and represent an elevation map of various buildings where the width of each bar/building is 1, Find out how much water can be saved in between them when it rains.

Array

Find K Pairs with Smallest Sum Java Solution

Problem Statement Given two integer arrays, arr1 and arr2, find K pairs of elements such that (x,y) where x is the value from the first array and y is the value from the second array who sum is the smallest. For example, give

Array

Find Two Numbers in an Array Which Sum Up to K

Problem Statement Given an array of integers, find out two indices such that the sum of the numbers at that indices matches K. For example, {4, 6, 8, 1, 9} and K = 15, the output would be [1,4] Solution Explanation The questions is

Array

Check If a Sudoku is Valid

Problem Statement Determine if a sudoku is Valid. Solution Explanation Given a sudoku grid, we need to verify if the already filled in numbers doesn't violate the sudoku rules. The rules are very simple, Each row has numbers from 1-9 and no repitions Each

Math

Generate all Factor Combinations

Problem Statement Given a number 'n', generate all factor combinations. For example, when n=24, the result would be [[2, 3, 3], [2, 9], [3, 6]] Solution Explanation As we know, every integer can be formed by product or multiplication of some numbers. These

Linked List

Check if a LinkedList has a cycle

Problem Statement Given a single linked list, verify if the list has a cycle. A linked list has a cycle if a node's reference points back to an earlier node in the chain. Example: 1 -> 2 -> 3 -> 4

Array

Best Time to Buy and Sell Stock

Problem Statement Given an array 'stocks' in which each value at index 'i' is the stock price on day 'i', Find the maximum profit you can make by performing atmost one Buy and one Sell on these stock prices. Example 1: Input: [10, 1,

Leetcode Medium

Find Inorder Successor in a Binary Search Tree

Problem Statement Given a binary search tree and the value of a certain node, find the next node in the inorder sequence after the given node. Solution Explanation The important information here is that the tree is a binary search tree and we need

Linked List

Linked List Implementation Java

Problem Statement Implement a single linked list in Java Solution Explanation Linked List is one of the heavily used data structure in computer programming. It is basically a linear collection of data elements and is represented by a group of nodes each pointing to

Array

Number of Islands Leetcode

Problem Statement Given a 2d grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are

Math

Find the Celebrity

Problem Statement Suppose you are at a party with n people (labeled from 0 to n - 1) and among them, there may exist one celebrity. The definition of a celebrity is that all the other n - 1 people know him/her but

Array

Three Sum(3Sum) Leetcode

Problem Statement Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero. Solution Explanation Given an integer array like below,

Array

Meeting Rooms Leetcode

Problem Statement Given an array of meeting time intervals consisting of start and end times [[s1,e1],[s2,e2],...] (si < ei), find the minimum number of conference rooms required. For example, Given [[0, 30],[5, 10],[15, 20]], return 2. Solution Explanation The

String

Decode Ways Leetcode

Problem Statement A message containing letters from A-Z is being encoded to numbers using the following mapping: 'A' -> 1 'B' -> 2 ... 'Z' -> 26 Given an encoded message containing digits, determine the total number of ways to decode it.

String

Letter Combinations of a Phone Number

Problem Statement Given a digit string, return all possible letter combinations that the number could represent. Input:Digit string "23" Output: ["ad", "ae", "af", "bd", "be", "bf", "cd"

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