Given an array of integers, 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once. Find all the elements that appear twice in this array. Could you do it without extra space and in O(n) runtime? Example: Input: [4,3,2,7,8,2,3,1] Output: [2,3] Approach When find a number i, flip the number at position i-1 to negative.If …

# Category: Programming

# How Many Numbers Are Smaller Than the Current Number

Given the array nums, for each nums[i] find out how many numbers in the array are smaller than it. That is, for each nums[i] you have to count the number of valid j's such that j != i and nums[j] < nums[i]. Return the answer in an array. Example 1: Input: nums = [8,1,2,2,3] Output: [4,0,1,1,3] Explanation: For nums[0]=8 there exist four smaller numbers than …

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# Minimum Remove to Make Valid Parentheses

Introduction In this article, we will see about Minimum Remove to Make Valid Parentheses. We have to remove the minimum number of parentheses to make a string with valid parentheses. BACKGROUND Day 15 of 100 Days of Leetcode Programming Challenge. This problem tests our knowledge in the Stack data structure. LANGUAGE I took C# programming language …

# Alphabet Board Path

INTRODUCTION In this article, we will see about Alphabet Board Path. It is one of the interesting problem, find Alphabet Board Path. BACKGROUND Day 14 of 100 Days of Leetcode Programming Challenge. This is one of the top Leetcode Problem. This problem tests our logical skills. LANGUAGE I took C# programming language to solve this …

# How to Reorganize String?

INTRODUCTION In this article, we will see about How to Reorganize String? It is one of the interesting problem, Reorganizing string. Background Day 13 of 100 Days of Leetcode Programming Challenge. This is one of the top Leetcode Problem. This problem tests our knowledge in string manipulations and hashing. Related Problems Top K Frequent ElementsHow …

# How to Sort Characters By Frequency?

Introduction In this article, we will see about How to sort characters based upon frequency? Background Day 12 of 100 Days of Leetcode Programming Challenge. This is one of the top Leetcode Problem. This problem tests our knowledge in Map data structure and Sorting. Language I took C# programming language to solve this problem. Since …

# Maximum Depth of Binary Tree

In this article, I explain about how to find the Maximum Depth of Binary Tree which is also called as Height of Binary Tree. Given a binary tree, find its maximum depth. The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node. Note: A …

# Look and Say (Count and Say) Sequence

Day 10 Find the nth term in Count and Say Sequence. The Count and Say sequence is the sequence of below integers: "1" "11" "21" "1211" "111221" "312211" "13112221" "1113213211" "31131211131221" "13211311123113112211" "11131221133112132113212221" "3113112221232112111312211312113211" "1321132132111213122112311311222113111221131221" "11131221131211131231121113112221121321132132211331222113112211" "311311222113111231131112132112311321322112111312211312111322212311322113212221" For example: If you have "1", the next line is "11".If you have "11", the next line is …

# Find the Missing Number in an Array

In this article, I explained about how to find the missing number in an array. Given an array containing n distinct numbers taken from 0, 1, 2, ..., n, find the one that is missing from the array. Example 1: Input: [3,0,1] Output: 2 Example 2: Input: [9,6,4,2,3,5,7,0,1] Output: 8 Note:Your algorithm should run in linear run time …

# Squares of a Sorted Array

Day 8 Welcome to 100 Days of Leetcode Challenge. Given an array of integers A sorted in non-decreasing order, return an array of the squares of each number, also in sorted non-decreasing order. Example 1: Input: [-4,-1,0,3,10] Output: [0,1,9,16,100] Example 2: Input: [-7,-3,2,3,11] Output: [4,9,9,49,121] Note: 1 <= A.length <= 10000-10000 <= A[i] <= 10000A is sorted in non-decreasing order. …

# How to Reverse Bits – Bit Manipulation

Reversing bits is one of the popular problem. How to reverse bits? In this article, we going to see about how to reverse bits in an efficient way. Reversing bits tests out understanding about bits. One of the top leetcode problem in bits section. Let's see our given problem, Reverse bits of a given 32 …

# Rotate Array

Hi Geeks! Welcome to 100 Days of Leetcode Challenge. DAY 6 In this article, I'm going to explain about how to rotate an array efficiently. This is nothing but just playing with Array. Here is our given problem, Given an array, rotate the array to the right by k steps, where k is non-negative. Example 1: Input: [1,2,3,4,5,6,7] and k …

# Sqrt(x)

Hi Geeks! Welcome to 100 Days of Leetcode Challenge. Day 5 Today we going to see about implementation of sqrt(x). Let's jump into our given question, Implement int sqrt(int x). Compute and return the square root of x, where x is guaranteed to be a non-negative integer. Since the return type is an integer, the decimal digits are truncated and only …

# Evaluate Reverse Polish Notation

Hi Geeks! Welcome to 100 Days of Leetcode Challenge. Day 4 Evaluate the value of an arithmetic expression in Reverse Polish Notation. Valid operators are +, -, *, /. Each operand may be an integer or another expression. Note: Division between two integers should truncate toward zero.The given RPN expression is always valid. That means the expression would always evaluate …

# Finding all Subsets of a given set

Hi Geeks! Welcome to 100 Days Leetcode Challenge. Day 3 In this article, I'll explain about how to find all the subsets of a given set(power set). Here is our given problem, Given a set of distinct integers, nums, return all possible subsets. Note: The solution set must not contain duplicate subsets. Example: Input: nums = [1,2,3] Output: [ [3], …

# Product of Array Except Self

Hi Geeks! Welcome to 100 Days Leetcode Challenge. Day 2 Here is our given problem, Given an array nums of n integers where n > 1, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i]. Example: Input: [1,2,3,4] Output: [24,12,8,6] Note: Please solve it without division and in O(n). Follow up:Could you solve it with constant space complexity? (The output array does …

# Top K Frequent Elements

Hi Geeks! Welcome to 100 Days Leetcode Challenge. Day 1 Here is our given problem, Given a non-empty array of integers, return the k most frequent elements. Example 1: Input: nums = [1,1,1,2,2,3], k = 2 Output: [1,2] Example 2: Input: nums = [1], k = 1 Output: [1] Note: You may assume k is always valid, 1 ≤ k ≤ …

# 100 Days Leetcode Challenge

Hi Geeks! Welcome to 100 Days Leetcode challenge. In these days, we going to solve Leetcode's top 100 data structures and algorithm problems. Purpose of 100 Days Leetcode Challenge The main purpose of this challenge is, as a Software Developer we should have a strong command over the algorithms and data structures.Solving these problems daily, …

# Reverse an Integer Digits

In this article, we going to see about How to Reverse an Integer? Given a 32-bit signed integer, reverse digits of an integer. Example 1: Input: 123 Output: 321 Example 2: Input: -123 Output: -321 Example 3: Input: 120 Output: 21 Note:Assume we are dealing with an environment which could only store integers within the …

# Binary Search – Best Explanation

Hi Geeks! Today, we going to see about Binary Search Algorithm to search an element in an array. When an array is sorted, we can apply the binary search algorithm. There are two ways to search an element in an array. Linear SearchBinary Search Linear Search When an array is unsorted, we can apply the …

# 13) Remove Nth Node From End of List

Hi friends, in this article we going to see how to remove the Nth node from end of the list. Here is our given problem, Given a linked list, remove the n-th node from the end of list and return its head. Example: Given linked list: 1->2->3->4->5, and n = 2. After removing the second node …

# 12) Linked List – Add Two Numbers

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list. You may assume the two numbers do not contain any leading zero, except the number 0 itself. Example: Input: (2 -> …

# 11) Palindrome Linked List

This is our given problem, Given a singly linked list, determine if it is a palindrome. Example 1: Input: 1->2 Output: false Example 2: Input: 1->2->2->1 Output: true Follow up:Could you do it in O(n) time and O(1) space? How can we APPROACH this problem? By using two ways, we can solve this problem, Slow …

# 10) Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists. Example: Input: 1->2->4, 1->3->4 Output: 1->1->2->3->4->4 Explanation L1 = 1->4 L2 = 2->3 Output = 1->2->3->4 Create a dummy node. ListNode dummy = new ListNode(0); //dummy = …

# 9) Linked List Cycle II

In this article we going to see about how to Detect Loop in a Linked List and Return the Loop Node. Below is our given problem from Leetcode, Given a linked list, return the node where the cycle begins. If there is no cycle, return null. To represent a cycle in the given linked list, we …

# 2020 – Consistency is the Key

I always used to say, consistency is the key to success. We going to practice the consistency in programming. Why Consistency in programming? Today, in the IT industry, majority of people don't have good command over the subject. Recent studies proven that, there is huge chuck of software engineers are unfit for software development jobs. …

# C# Program to Validate IP Address

Hi geeks, in this article we going to see about the Leetcode's Validate Ip Address Problem. This is one of the important interview question. There are different ways to solve this problem like Naive Approach, Straight Forward Approach, etc. But I solved this problem in a efficient way by using Microsoft framework's packages like System.Net, …

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# Minimum Absolute Difference

Given an array of distinct integers arr, find all pairs of elements with the minimum absolute difference of any two elements. Return a list of pairs in ascending order(with respect to pairs), each pair [a, b] follows a, b are from arra < bb - a equals to the minimum absolute difference of any two elements in arr Example 1: Input: arr = [4,2,1,3] Output: [[1,2],[2,3],[3,4]] …

# How to Improve Programming Skills?

Basically, you have to understand, programming is easy when it's followed by proper guidance and practice. Constant practice makes you a master in this field. Be consistent in practice then you will see result. There are many resources available in online to develop your programming skills. I'm going to share the important resources which are very useful and …

# About

Hi Geeks, My name is Meikandanathan. I'm 21 years old and live in India, with my family. I'm a part time blogger and currently working as a Software Developer at Kovai.co. Gaining knowledge, is the first step to wisdom. Sharing it, is the first step to humanity.I created this website to share my technical ideas …