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I did the Leetcode grind, and got offers from Uber, Facebook, LinkedIn, Nextdoor and WalmartLabs. Here are the problems that I think are crucial to developing a strong understanding of interview question patterns.
Also must see: Arden Dertat’s list.
Problems are grouped according to the concepts required to solve them.
17. Letter Combinations of a Phone Number
247. Strobogrammatic Number II
267. Palindrome Permutation II
347. Top K Frequent Elements (Multiple ways to do it, but bucket sort is important.)
215. Kth Largest Element in an Array
138. Copy List with Random Pointer
173. Binary Search Tree Iterator (Important is achieving the average run-time).
341. Flatten Nested List Iterator
535. Encode and Decode TinyURL
158. Read N Characters Given Read4 II - Call multiple times (also checkout the predecessor to this problem)
211. Add and Search Word - Data structure design
208. Implement Trie (Prefix Tree)
Tip: Try coming up with the recursive logic first. Converting that to DP is the easy part.
10. Regular Expression Matching
300. Longest Increasing Subsequence
304. Range Sum Query 2D - Immutable
416. Partition Equal Subset Sum
516. Longest Palindromic Subsequence
583. Delete Operation for Two Strings
Graph related problems are frequently asked, and there are more quality problems out there that you should explore.
215. Kth Largest Element in an Array
Another important category, try to do more problems here.
Quality reading material on this category: Chapter 6 in Competitive Programmer’s Handbook
3. Longest Substring Without Repeating Characters
438. Find All Anagrams in a String
340. Longest Substring with At Most K Distinct Characters
Good reading on this topic: Sourab Reddy’s Medium post
It is a good idea to practice doing preorder, inorder and postorder traversals both iteratively and recrusively. Helps a great deal with approaching tree problems.
Most tree problems are simple tweaks on a type of traversal, or simple DFS/BFS.
98. Validate Binary Search Tree
236. Lowest Common Ancestor of a Binary Tree
103. Binary Tree Zigzag Level Order Traversal
102. Binary Tree Level Order Traversal
199. Binary Tree Right Side View
94. Binary Tree Inorder Traversal
230. Kth Smallest Element in a BST
144. Binary Tree Preorder Traversal
515. Find Largest Value in Each Tree Row
141. Linked List Cycle The O(N) with constant space trick is intresting and has applications in many Linked List problems.
121. Best Time to Buy and Sell Stock
238. Product of Array Except Self
33. Search in Rotated Sorted Array
19. Remove Nth Node From End of List
636. Exclusive Time of Functions
150. Evaluate Reverse Polish Notation
29. Divide Two Integers Careful about overflows!
426. Convert Binary Search Tree to Sorted Doubly Linked List
166. Fraction to Recurring Decimal
34. Find First and Last Position of Element in Sorted Array
209. Minimum Size Subarray Sum
852. Peak Index in a Mountain Array
325. Maximum Size Subarray Sum Equals k