Data Structures & Algorithms

Arrays

Linear Scan

• Majority Element-I (Easy)
• Kadane's Algorithm (Medium)
• Majority Element-II (Medium)
• Maximum Product Subarray in an Array (Medium)

Two Pointers

• Sort an array of 0's 1's and 2's (Medium)
• 3 Sum (Medium)
• Next Permutation (Medium)
• 4 Sum (Medium)
• Merge two sorted arrays without extra space (Easy)
• Trapping Rainwater (Hard)

Divide and Conquer

• Count Inversions (Medium)
• Reverse Pairs (Hard)

Hashing

Hashing & Prefix Sums

• Two Sum (Easy)
• Longest Consecutive Sequence in an Array (Medium)
• Longest subarray with sum K (Medium)
• Count subarrays with given sum (Medium)
• Count subarrays with given xor K (Medium)

Binary Search

Binary Search

• Find peak element (Medium)
• Find minimum in Rotated Sorted Array (Medium)
• Search in rotated sorted array-II (Medium)
• Single element in sorted array (Medium)
• Search in 2D matrix - II (Medium)
• Find Peak Element - II (Medium)

Search on Answer

• Find Nth root of a number (Easy)
• Koko eating bananas (Medium)
• Aggressive Cows (Medium)
• Book Allocation Problem (Hard)
• Matrix Median (Medium)

Partition Search

• Kth element of 2 sorted arrays (Hard)
• Median of 2 sorted arrays (Hard)

Sliding Window and Two Pointers

Sliding Window

• Longest Substring Without Repeating Characters (Medium)
• Maximum Points You Can Obtain from Cards (Medium)
• Max Consecutive Ones III (Medium)
• Longest Repeating Character Replacement (Medium)
• Longest Substring With At Most K Distinct Characters (Medium)
• Minimum Window Substring (Hard)

Counting Windows

• Number of Substrings Containing All Three Characters (Medium)
• Binary Subarrays With Sum (Medium)
• Count number of Nice subarrays (Medium)

Recursion and Backtracking

Subsets & Combinations

• Power Set (Medium)
• Generate Parentheses (Medium)
• Letter Combinations of a Phone Number (Medium)
• Combination Sum (Medium)
• Combination Sum II (Medium)
• Subsets II (Medium)
• Palindrome partitioning (Medium)

Backtracking

• Word Search (Medium)
• N Queen (Hard)
• Sudoku Solver (Hard)

Linked List

Fast & Slow Pointers

• Find Middle of Linked List (Easy)
• Find the intersection point of Y LL (Easy)
• Check if LL is palindrome or not (Easy)
• Detect a loop in LL (Easy)
• Remove Nth node from the back of the LL (Medium)
• Find the starting point in LL (Medium)
• Length of loop in LL (Easy)

Reversal & Rewiring

• Reverse a LL (Easy)
• Merge two Sorted Lists (Easy)
• Sort a Linked List of 0's 1's and 2's (Medium)
• Add two numbers in Linked List (Medium)
• Rotate a LL (Medium)
• Sort LL (Medium)
• Clone a LL with random and next pointer (Medium)
• Reverse LL in group of given size K (Hard)
• Flattening of LL (Hard)

Stack and Queues

Monotonic Stack / Queue

• Next Greater Element (Easy)
• Next Greater Element - 2 (Medium)
• Stock span problem (Medium)
• Sum of Subarray Minimums (Medium)
• Sum of Subarray Ranges (Medium)
• Remove K Digits (Medium)
• Sliding Window Maximum (Hard)
• Largest rectangle in a histogram (Hard)
• Maximum Rectangles (Hard)

Data Structure Design

• Implement Min Stack (Medium)
• Asteroid Collision (Medium)
• Celebrity Problem (Medium)
• LRU Cache (Medium)
• LFU Cache (Hard)

Greedy Algorithms

Greedy

• Jump Game - I (Medium)
• Valid Parenthesis Checker (Medium)
• Candy (Hard)

Intervals & Scheduling

• N meetings in one room (Easy)
• Insert Interval (Medium)
• Non-overlapping Intervals (Medium)
• Minimum number of platforms required for a railway (Medium)
• Job sequencing Problem (Medium)

Heaps

Heap / Priority Queue

• Heapify Algorithm (Easy)
• Build heap from a given Array (Easy)
• Implement Min Heap (Medium)
• K-th Largest element in an array (Medium)
• Find Median from Data Stream (Hard)

Binary Trees

BFS

• Level Order Traversal (Medium)
• Maximum Width of BT (Medium)
• Right/Left View of BT (Medium)
• Top View of BT (Medium)
• Print all nodes at a distance of K in BT (Medium)
• Minimum time taken to burn the BT from a given Node (Medium)
• Vertical Order Traversal (Hard)

DFS / Tree DP

• Print root to leaf path in BT (Easy)
• Diameter of Binary Tree (Easy)
• Lowest Common Ancestor in BT (Medium)
• Boundary Traversal (Medium)
• Construct a BT from Preorder and Inorder (Medium)
• Morris Inorder Traversal (Easy)
• Maximum path sum (Hard)
• Serialize and De-serialize BT (Hard)

Binary Search Trees

Inorder Traversal

• Insert a given node in BST (Medium)
• LCA in BST (Medium)
• Delete a node in BST (Medium)
• Inorder successor and predecessor in BST (Medium)
• Kth Smallest and Largest element in BST (Medium)
• Check if a tree is a BST or not (Medium)
• Construct a BST from a preorder traversal (Medium)
• Two sum in BST (Easy)
• Correct BST with two nodes swapped (Medium)
• Largest BST in Binary Tree (Medium)

Graphs

BFS / DFS

• Flood fill algorithm (Easy)
• Number of islands (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 (Medium)
• Bipartite graph (Medium)

Ordering & Connectivity

• Detect a cycle in a directed graph (Medium)
• Topological sort or Kahn's algorithm (Medium)
• Course Schedule II (Medium)
• Alien Dictionary (Hard)
• Kosaraju's algorithm (Hard)
• Bridges in graph (Hard)
• Articulation point in graph (Hard)

Shortest Path

• Shortest path in undirected graph with unit weights (Medium)
• Shortest path in DAG (Medium)
• Dijkstra's algorithm (Medium)
• Path with minimum effort (Medium)
• Cheapest flight within K stops (Medium)
• Bellman ford algorithm (Medium)
• Floyd warshall algorithm (Medium)
• Word ladder I (Hard)
• Word ladder II (Hard)

DSU / MST

• Disjoint Set (Medium)
• Find the MST weight (Medium)
• Number of operations to make network connected (Medium)
• Number of islands II (Hard)
• Making a large island (Hard)

Dynamic Programming

State Transition DP

• Frog jump with K distances (Medium)
• House robber (Medium)
• Ninja's training (Medium)
• Unique paths II (Medium)
• Best time to buy and sell stock with transaction fees (Medium)
• Best time to buy and sell stock IV (Hard)

Knapsack DP

• 0 and 1 Knapsack (Medium)
• Partition a set into two subsets with minimum absolute sum difference (Medium)
• Target sum (Medium)
• Coin change II (Medium)

Sequence DP

• Longest common subsequence (Medium)
• Longest common substring (Medium)
• Longest palindromic subsequence (Medium)
• Longest Increasing Subsequence (Medium)
• Number of Longest Increasing Subsequences (Medium)
• Edit distance (Medium)
• Wildcard matching (Hard)

Partition DP

• Matrix chain multiplication (Hard)
• Palindrome partitioning II (Hard)

Tries

Trie

• Trie Implementation and Advanced Operations (Medium)
• Longest Word with All Prefixes (Medium)
• Number of distinct substrings in a string (Medium)
• Maximum XOR of two numbers in an array (Medium)
• Maximum Xor with an element from an array (Hard)

Strings

String Matching

• Rabin Karp Algorithm (Medium)
• Z function (Hard)
• KMP Algorithm or LPS array (Easy)
• Shortest Palindrome (Hard)

Bit Manipulation

Bit Manipulation

• Power Set Bit Manipulation (Medium)
• Single Number - II (Medium)
• Single Number - III (Medium)
• Find the repeating and missing number (Easy)

Mathematics

Number Theory

• Print all primes till N (Medium)