All_SDE_sheet.md

All SDE sheet

Algorithms

Arrays & Strings

• Two Sum variants (indices, count pairs, unique pairs)
• Best Time to Buy and Sell Stock (I/II/with cooldown/with fee)
• Product of Array Except Self (zeros & negatives)
• Longest Substring Without Repeating Characters
• Minimum Window Substring
• Longest Palindromic Substring
• Palindromic Substrings (count)
• Valid Anagram / Group Anagrams
• Rotate Array / String Rotation check
• Merge Intervals / Insert Interval
• Non-overlapping Intervals (erase overlaps)
• Meeting Rooms I/II
• Subarray Sum Equals K (positive & mixed)
• Maximum Subarray (Kadane) + circular variant
• Find Pivot Index / Equilibrium index
• Gas Station (circular tour)
• Container With Most Water
• Trapping Rain Water (two pointers & stack)
• 3Sum / 4Sum / 3Sum Closest
• Remove Duplicates from Sorted Array (I/II)
• Dutch National Flag (sort colors)
• Shortest Unsorted Continuous Subarray
• Word Break (I/II) – DP vs Trie
• Longest Common Prefix
• String to Integer (atoi) – edge cases
• Zigzag Conversion / String Compression
• Multiply Strings / Add Strings / Big integer
• Valid Parentheses / Minimum Add to Make Valid
• Backspace String Compare
• Find All Anagrams in a String
• Ransom Note / Construct String from Another
• Is Subsequence / Shortest Way to Form String
• Minimum Remove to Make Valid Parentheses
• Longest Repeating Character Replacement
• Sliding Window Maximum (deque)
• Find Minimum in Rotated Sorted Array (with duplicates)
• Search in Rotated Sorted Array (I/II)
• Find First and Last Position of Element (binary search)
• Longest Consecutive Sequence
• Set Matrix Zeroes (in-place)
• Spiral Matrix (I/II)
• Rotate Image (in-place 2D transform)
• Game of Life (in-place encoding)
• Word Search (board backtracking)
• Distinct Subsequences (count ways)

Hash / Stack / Queue

• LRU Cache (design) – hashmap + doubly linked list
• LFU Cache (design) – freq lists
• Min Stack / Max Stack (getMin in O(1))
• Evaluate Reverse Polish Notation
• Basic Calculator I/II/III (parentheses, precedence)
• Valid Parentheses with wildcards (* as ) or empty)
• Next Greater Element (I/II) – monotonic stack
• Daily Temperatures – monotonic stack
• Stock Span / Online Stock Span
• Queue using Stacks / Stack using Queues
• Implement Circular Queue / Deque
• Design Hit Counter / Rate Limiter
• Design Browser History (two stacks)
• Decode String (k[encoded])
• Remove K Digits to form smallest number
• Asteroid Collision (stack)
• Candy Crush / String Explosion
• Largest Rectangle in Histogram
• Maximal Rectangle in Binary Matrix
• Celebrity Problem / Find the Town Judge

Linked Lists

• Reverse Linked List (I/II partial groups of k)
• Merge Two Sorted Lists / Merge K Sorted Lists (heap)
• Add Two Numbers (forward & reverse order)
• Remove Nth Node From End
• Reorder List / Odd Even Linked List
• Linked List Cycle (detect & entry point)
• Copy List with Random Pointer
• Partition List by value
• Sort List (merge sort on list)
• Rotate List / Swap Nodes in Pairs

Trees & BST

• Binary Tree Inorder/Preorder/Postorder Traversal (iterative & recursive)
• Level Order Traversal / Zigzag Level Order
• Diameter of Binary Tree
• Balanced Binary Tree / Height Balanced Check
• Maximum Depth / Minimum Depth of Binary Tree
• Path Sum I/II/III (count paths)
• Lowest Common Ancestor (Binary Tree)
• Lowest Common Ancestor (BST)
• Serialize and Deserialize Binary Tree (design)
• Construct Tree from Preorder & Inorder / Postorder
• Binary Tree Right Side View / Left View
• Flatten Binary Tree to Linked List
• Validate Binary Search Tree (bounds)
• Kth Smallest / Largest in BST
• Convert Sorted Array/List to BST
• Inorder Successor/Predecessor in BST
• Range Sum of BST / Trim BST
• Recover Binary Search Tree (swap fix)
• Count Complete Tree Nodes (binary search on tree)
• Sum of Distances in Tree (tree DP re-rooting)

Graphs

• Number of Islands (DFS/BFS/Union-Find)
• Clone Graph (BFS/DFS)
• Course Schedule I/II (topological sort)
• Alien Dictionary (topo + lexicographic constraints)
• Word Ladder I/II (BFS + heuristics)
• Pacific Atlantic Water Flow / Surrounded Regions
• Walls and Gates / Rotting Oranges
• Shortest Path in Binary Matrix / Maze solver
• Network Delay Time (Dijkstra)
• Cheapest Flights Within K Stops (Bellman-Ford/DP)
• Reconstruct Itinerary (Hierholzer / Eulerian path)
• Redundant Connection (Union-Find)
• Graph Valid Tree / Count Components
• Kruskal / Prim Minimum Spanning Tree (design question)
• Evaluate Division (graph with weights)
• Accounts Merge (Union-Find)
• Critical Connections (Tarjan bridges)
• Course Scheduling with prerequisites window (advanced topo)
• Minimum Height Trees
• Bipartite Graph Check / Possible Bipartition

Searching & Sorting

• Quickselect (Kth Largest Element)
• Top K Frequent Elements (heap/bucket)
• Sort Colors (DNF) / 3-way partition
• Merge K Sorted Arrays (heap) / external sort idea
• Search a 2D Matrix (I/II)
• Find Peak Element / Mountain Array peak
• Median of Two Sorted Arrays (binary search on partitions)
• Sort Characters By Frequency / Relative Sort Array
• H-Index / H-Index II
• Find Duplicate Number (Floyd vs binary search on answer)

Heaps & Greedy

• Meeting Rooms II (min-heap)
• Task Scheduler (cooldown) – greedy + heap
• Reorganize String / Rearrange String k Distance Apart
• IPO / Maximize Capital (two heaps)
• Hand of Straights / Divide Array in Sets of K
• Boats to Save People / Assign Cookies
• Gas Station (greedy proof)
• Jump Game I/II (greedy farthest reach)
• Partition Labels
• Minimum Number of Arrows to Burst Balloons
• Non-overlapping Intervals (erase minimum)
• Candy (two-pass greedy)
• Lemonade Change
• Split Array Largest Sum (binary search + greedy check)
• Minimum Cost to Connect Sticks (heap)

Dynamic Programming

• Climbing Stairs / Min Cost Climbing Stairs
• House Robber I/II/III
• Coin Change (min coins, count combinations)
• Longest Increasing Subsequence (O(n log n))
• Edit Distance (Levenshtein)
• Decode Ways I/II
• Unique Paths I/II (with obstacles)
• Partition Equal Subset Sum / Target Sum
• Burst Balloons (interval DP)
• Palindromic Substrings / Longest Palindromic Subsequence
• Regular Expression Matching / Wildcard Matching
• Best Time to Buy/Sell Stock with K transactions
• Word Break DP (count ways vs boolean)
• Interleaving String
• Scramble String
• Matrix Chain Multiplication / Minimum Score Triangulation
• Paint House I/II (with k colors)
• Minimum Falling Path Sum / Triangle
• Cherry Pickup / Grid DP with states
• Knapsack 0/1 & Unbounded variants (pattern)

Math / Bit / Geometry

• Reverse Bits / Number of 1 Bits
• Single Number I/II/III (bitwise)
• Missing Number / Find All Missing / Duplicates
• Power of Two/Three/Four / Fast Pow (binary exponentiation)
• Count Primes / Sieve of Eratosthenes
• Greatest Common Divisor / Euclid / LCM problems
• Happy Number / Ugly Number / Super Ugly Number
• Rectangle Overlap / Line Sweep basics
• Random Pick with Weight / Reservoir Sampling
• Kth Smallest in Multiplication Table (binary search on answer)

System Design

• Design a URL Shortener
• Design a News Feed / Timeline
• Design a Rate Limiter (per user/IP) – token bucket
• Design a Key-Value Store (caching + persistence)
• Design an E-commerce Cart & Checkout
• Design a Messaging/Chat System (WhatsApp-lite)
• Design a File Storage Service (Dropbox/Google Drive)
• Design a Web Crawler
• Design a Ride-Hailing/Dispatch System
• Design a Logging & Metrics System
• Design a Notification Service (email/SMS/push)
• Design a Payment System (idempotency, retries)
• Design a Search Autocomplete
• Design a Video Streaming Platform (Netflix-lite)
• Design a Pastebin
• Design a Social Graph (follow/unfollow, recommendations)
• Design a Leaderboard (time-decay, top-N)
• Design a Distributed Job Queue
• Design a Real-time Analytics Pipeline
• Design a Feature Flag Service

Behavioral (Amazon/Google-style LPs)

• Tell me about a time you owned an ambiguous problem end-to-end.(Ownership)
• Describe a situation you disagreed with a senior engineer and what happened. (Disagree & Commit)
• Tell me about a time you improved performance or reduced cost. (Deliver Results)
• Give an example when you prioritized customer needs over engineering preferences. (Customer Obsession)
• Tell me about a production incident you handled—root cause andprevention. (Dive Deep)
• Describe a time you moved fast with incomplete information.(Bias for Action)
• Tell me about mentoring a teammate and the impact.(Hire/Develop the Best)
• Describe a time you simplified a complex system or process.(Invent & Simplify)
• Tell me about a failure—what did you learn and change? (Learn & Be Curious)
• How do you handle conflicting deadlines across teams? (Earn Trust)