Problem Categories

Selection Sort Easy
Bubble Sort Easy
Insertion Sorting Easy
Merge Sorting Medium
Quick Sorting Easy

Linear Search Easy
Largest Element Easy
Second Largest Element Easy
Maximum Consecutive Ones Easy
Left Rotate Array by One Easy
Left Rotate Array by K Places Easy
Move Zeros to End Easy
Remove duplicates from sorted array Easy
Find missing number Easy
Union of two sorted arrays Easy
Intersection of two sorted arrays Easy
Leaders in an Array Medium
Print the matrix in spiral manner Medium
Rearrange array elements by sign Medium
Pascal's Triangle Medium
Rotate matrix by 90 degrees Medium
Two Sum Medium
3 Sum Medium
4 Sum Medium
Sort an array of 0's 1's and 2's Medium
Kadane's Algorithm Medium
Majority Element-I Hard
Majority Element-II Hard
Find the repeating and missing number Hard
Count Inversions Hard
Reverse Pairs Hard
Maximum Product Subarray in an Array Hard
Merge two sorted arrays without extra space Hard
Maximum Consecutive Good Numbers Easy
Set difference of two arrays Easy
Number of Jumps Easy

Longest Consecutive Sequence in an Array Hard
Longest subarray with sum K Hard
Count subarrays with given sum Hard
Count subarrays with given xor K Hard
Count of Subarrays with Sum Divisible by K Easy
Group Words by Anagrams Easy
Maximum Points on a Line Easy

Search X in sorted array Easy
Lower Bound Easy
Upper Bound Easy
Search insert position Easy
Floor and Ceil in Sorted Array Easy
First and last occurrence Easy
Search in rotated sorted array-I Easy
Search in rotated sorted array-II Easy
Find minimum in Rotated Sorted Array Easy
Find out how many times the array is rotated Easy
Single element in sorted array Medium
Find square root of a number Medium
Find Nth root of a number Medium
Find the smallest divisor Medium
Koko eating bananas Medium
Minimum days to make M bouquets Medium
Aggressive Cows Hard
Book Allocation Problem Hard
Find peak element Hard
Median of 2 sorted arrays Hard
Minimise max distance to gas stations Hard
Kth element of 2 sorted arrays Hard
Split array - largest sum Hard
Find row with maximum 1's Hard
Search in a 2D matrix Hard
Search in 2D matrix - II Hard
Find Peak Element Hard
Matrix Median Hard
Cleaning Windows Easy
Neighbours within k distance Easy
Z-Score Easy

Pow(x,n) Easy
Generate Paranthesis Easy
Power Set Easy
Check if there exists a subsequence with sum K Easy
Count all subsequences with sum K Easy
Combination Sum Medium
Combination Sum II Medium
Subsets I Medium
Subsets II Medium
Combination Sum III Medium
Letter Combinations of a Phone Number Hard
Palindrome partitioning Hard
Word Search Hard
N Queen Hard
Rat in a Maze Hard
M Coloring Problem Hard
Sudoko Solver Hard
Different Series Easy
Combination XOR Easy
Find Distinct Expressions Easy

Introduction to Singly LinkedList
Traversal in Linked List Easy
Deletion in Linked List
Insertion in Linked List
Deletion of the head of LL Easy
Deletion of the tail of LL Easy
Deletion of the Kth element of LL Easy
Delete the element with value X Easy
Insertion at the head of LL Easy
Insertion at the tail of LL Easy
Insertion at the Kth position of LL Easy
Insertion before the value X in LL Easy
Introduction to Doubly LL
Deletion in Doubly LL
Insertion in DLL
Convert Array to DLL Easy
Delete head of DLL Easy
Delete Tail of DLL Easy
Delete Kth Element of DLL Easy
Removing given node in DLL Easy
Insert node before head in DLL Easy
Insert node before tail in DLL Easy
Insert node before (kth node) in DLL Easy
Insert before given node in DLL Easy
Add two numbers in LL Medium
Segregate odd and even nodes in LL Medium
Sort a LL of 0's 1's and 2's Medium
Remove Nth node from the back of the LL Medium
Reverse a LL Medium
Add one to a number represented by LL Medium
Check if LL is palindrome or not Medium
Find the intersection point of Y LL Medium
Detect a loop in LL Medium
Find the starting point in LL Medium
Length of loop in LL Medium
Delete the middle node in LL Medium
Reverse LL in group of given size K Hard
Rotate a LL Hard
Merge two Sorted Lists Hard
Flattening of LL Hard
Sort LL Hard
Clone a LL with random and next pointer Hard
Delete all occurrences of a key in DLL Hard
Remove duplicated from sorted DLL Hard
Remove bad elements in Linked List Easy
Segregate Nodes into 3 parts in LL Easy
Special Linked List Easy

Introduction to Bits and Tricks
Minimum Bit Flips to Convert Number Medium
Single Number - I Medium
Single Number - II Medium
Single Number - III Medium
Divide two numbers without multiplication and division Medium
Power Set Bit Manipulation Medium
XOR of numbers in a given range Medium
Count Set Cost Easy
Twin Numbers Easy
Odd Subsets Easy

Assign Cookies Easy
Lemonade Change Easy
Jump Game - I Easy
Shortest Job First Medium
Job sequencing Problem Medium
N meetings in one room Medium
Non-overlapping Intervals Medium
Insert Interval Medium
Minimum number of platforms required for a railway Medium
Valid Paranthesis Checker Hard
Candy Hard
Maximum XOR Length Easy
Un Palindromic Strings Easy
Maximum sum Easy

Theory
Maximum Points You Can Obtain from Cards Medium
Longest Substring Without Repeating Characters Hard
Max Consecutive Ones III Hard
Fruit Into Baskets Hard
Longest Substring With At Most K Distinct Characters Hard
Longest Repeating Character Replacement Hard
Minimum Window Substring Hard
Number of Substrings Containing All Three Characters Hard
Binary Subarrays With Sum Hard
Count number of Nice subarrays Hard
Max Odd Numbers in K Window Medium
Maximum Good Subarray Length Medium
Number of Subarrays with Or less than K Hard

Implementation using different DS
Implement Stack using Arrays Easy
Implement Queue using Arrays Easy
Implement Stack using Queue Easy
Implement Queue using Stack Easy
Implement stack using Linkedlist Easy
Implement queue using Linkedlist Easy
Balanced Paranthesis Easy
Next Greater Element Medium
Next Greater Element - 2 Medium
Asteroid Collision Medium
Sum of Subarray Minimums Medium
Sum of Subarray Ranges Medium
Remove K Digits Medium
Implement Min Stack Hard
Sliding Window Maximum Hard
Trapping Rainwater Hard
Largest rectangle in a histogram Hard
Maximum Rectangles Hard
Stock span problem Hard
Celebrity Problem Hard
LRU Cache Hard
LFU Cache Hard
Count Collisons Easy
Lexicographically Smallest String Easy
Maximum Value Of A Subarray Easy

Introduction
Preorder Traversal Easy
Inorder Traversal Easy
Postorder Traversal Easy
Level Order Traversal Easy
Pre, Post, Inorder in one traversal Easy
Maximum Depth in BT Medium
Check if two trees are identical or not Medium
Check for balanced binary tree Medium
Diameter of Binary Tree Medium
Maximum path sum Medium
Check for symmetrical BTs Medium
Zig Zag or Spiral Traversal Medium
Boundary Traversal Medium
Vertical Order Traversal Medium
Top View of BT Medium
Bottom view of BT Medium
Right/Left View of BT Medium
Print root to node path in BT Hard
LCA in BT Hard
Maximum Width of BT Medium
Print all nodes at a distance of K in BT Hard
Minimum time taken to burn the BT from a given Node Hard
Count total nodes in a complete BT Hard
Requirements needed to construct a unique BT Hard
Construct a BT from Preorder and Inorder Hard
Construct a BT from Postorder and Inorder Hard
Serialize and De-serialize BT Hard
Morris Inorder Traversal Hard
Morris Preorder Traversal Hard
Minimum Travel Cost Easy
Maximum subtree sum Easy
Tree Greatness Easy

Introduction to BST
Search in BST Easy
Floor and Ceil in a BST Easy
Insert a given node in BST Medium
Delete a node in BST Medium
Kth Smallest and Largest element in BST Medium
Check if a tree is a BST or not Medium
LCA in BST Medium
Construct a BST from a preorder traversal Medium
Inorder successor and predecessor in BST Medium
BST iterator Hard
Two sum in BST Hard
Correct BST with two nodes swapped Hard
Largest BST in Binary Tree Hard
Range Sum in BST Easy
Great Tree Medium

Heaps (Theory Video)
Heapify Algorithm Medium
Build heap from a given Array Medium
Implement Min Heap Medium
Implement Max Heap Medium
Check if an array represents a min heap Medium
Convert Min Heap to Max Heap Medium
Heap Sort Medium
K-th Largest element in an array Medium
Kth largest element in a stream of running integers Hard
K Nearest Integers Easy
Minimum Operations To Exceed Target Easy
Furthest Reachable Mountain Easy

Introduction to Graph
Connected Components Medium
Traversal Techniques Medium
Number of provinces Medium
Number of islands Medium
Flood fill algorithm Medium
Number of enclaves Medium
Rotten Oranges Medium
Distance of nearest cell having one Medium
Surrounded Regions Medium
Number of distinct islands Medium
Detect a cycle in an undirected graph Hard
Bipartite graph Hard
Topological sort or Kahn's algorithm Hard
Detect a cycle in a directed graph Hard
Find eventual safe states Hard
Course Schedule I Hard
Course Schedule II Hard
Alien Dictionary Hard
Shortest path in DAG Hard
Shortest path in undirected graph with unit weights Hard
Word ladder I Hard
Word ladder II Hard
Dijkstra's algorithm Hard
Print Shortest Path Hard
Shortest Distance in a Binary Maze Hard
Path with minimum effort Hard
Cheapest flight within K stops Hard
Minimum multiplications to reach end Hard
Number of ways to arrive at destination Hard
Bellman ford algorithm Hard
Floyd warshall algorithm Hard
Find the city with the smallest number of neighbors Hard
MST theory
Disjoint Set Hard
Find the MST weight Hard
Number of operations to make network connected Hard
Accounts merge Hard
Number of islands II Hard
Making a large island Hard
Most stones removed with same row or column Hard
Kosaraju's algorithm Hard
Bridges in graph Hard
Articulation point in graph Hard
Furthest Empty Plot From Buildings Easy
Find All Possible Tasks Easy
Reachable Nodes Before Destruction Easy

Introduction to DP
Climbing stairs Medium
Frog Jump Medium
Frog jump with K distances Medium
Maximum sum of non adjacent elements Medium
House robber Medium
Ninja's training Medium
Grid unique paths Medium
Unique paths II Medium
Minimum path sum in grid Medium
Triangle Medium
Cherry pickup II Medium
Best time to buy and sell stock Medium
Best time to buy and sell stock II Medium
Best time to buy and sell stock III Medium
Best time to buy and sell stock IV Medium
Best time to buy and sell stock with transaction fees Medium
Subset sum equals to target Hard
Partition equal subset sum Hard
Partition a set into two subsets with minimum absolute sum difference Hard
Count subsets with sum K Hard
Count partitions with given difference Hard
0 and 1 Knapsack Hard
Minimum coins Hard
Target sum Hard
Coin change II Hard
Unbounded knapsack Hard
Rod cutting problem Hard
Longest Increasing Subsequence Easy
Print Longest Increasing Subsequence Easy
Largest Divisible Subset Easy
Longest String Chain Easy
Longest Bitonic Subsequence Easy
Number of Longest Increasing Subsequences Easy
Longest common subsequence Hard
Longest common substring Hard
Longest palindromic subsequence Hard
Minimum insertions to make string palindrome Hard
Minimum insertions or deletions to convert string A to B Hard
Shortest common supersequence Hard
Distinct subsequences Hard
Edit distance Hard
Wildcard matching Hard
Matrix chain multiplication Hard
Minimum cost to cut the stick Hard
Burst balloons Hard
Palindrome partitioning II Hard
MEXX Easy
Buy Flowers Easy

Trie Implementation and Operations Hard
Trie Implementation and Advanced Operations Hard
Longest word with all prefixes Hard
Number of distinct substrings in a string Hard
Maximum XOR of two numbers in an array Hard
Maximum Xor with an element from an array Hard

Reverse every word in a string Hard
Minimum number of bracket reversals to make an expression balanced Hard
Count and say Hard
Rabin Karp Algorithm Hard
Z function Hard
KMP Algorithm or LPS array Hard
Shortest Palindrome Hard
Longest happy prefix Hard
Count Prefix Appearances
Distinct Substrings
Minimum Repetations

Print all primes till N Hard
Prime factorisation of a Number Hard
Count primes in range L to R Hard
Win or Lose Easy
Longest Factor Chain Easy

Insertion in DLL

Linked-List Fundamentals (Doubly LL) Go Ad-Free - ₹20/mo

Editorial

Watch the video for explanation, and to practice and read editorials around these problems, use the given below links.

Insert node before head in DLL
Insert node before tail in DLL
Insert node before (kth node) in DLL
Insert before given node in DLL

Notes

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