X Interview Questions — 52 DSA Problems

45 problems with full solutions in Python, Java, C++, JavaScript, Go, Rust.

Most frequently asked X LeetCode questions for software engineering interviews.

• Insert Delete GetRandom O(1) (MEDIUM) — Array, Hash Table, Math, Design, Randomized
• Flatten Nested List Iterator (MEDIUM) — Stack, Tree, Depth-First Search, Design, Queue, Iterator
• Trapping Rain Water (HARD) — Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack
• Design Twitter (MEDIUM) — Hash Table, Linked List, Design, Heap (Priority Queue)
• Tweet Counts Per Frequency (MEDIUM) — Hash Table, Binary Search, Design, Sorting, Ordered Set
• Merge Intervals (MEDIUM) — Array, Sorting
• Implement Trie (Prefix Tree) (MEDIUM) — Hash Table, String, Design, Trie
• Best Meeting Point (HARD) — Array, Math, Sorting, Matrix
• LRU Cache (MEDIUM) — Hash Table, Linked List, Design, Doubly-Linked List
• Investments in 2016 (MEDIUM) — Database
• Customer Placing the Largest Number of Orders (EASY) — Database
• Minimum Genetic Mutation (MEDIUM) — Hash Table, String, Breadth-First Search
• Minimum Number of Steps to Make Two Strings Anagram (MEDIUM) — Hash Table, String, Counting
• Validate IP Address (MEDIUM) — String
• Count Student Number in Departments (MEDIUM) — Database
• Rectangles Area (MEDIUM) — Database
• Invalid Tweets (EASY) — Database
• Tree Node (MEDIUM) — Database
• Number of Black Blocks (MEDIUM) — Array, Hash Table, Enumeration
• Masking Personal Information (MEDIUM) — String
• Design Authentication Manager (MEDIUM) — Hash Table, Linked List, Design, Doubly-Linked List
• Minimum Elements to Add to Form a Given Sum (MEDIUM) — Array, Greedy
• Binary Gap (EASY) — Bit Manipulation
• Finding the Users Active Minutes (MEDIUM) — Array, Hash Table
• Process Tasks Using Servers (MEDIUM) — Array, Heap (Priority Queue)
• Remove All Occurrences of a Substring (MEDIUM) — String, Stack, Simulation
• Count Sub Islands (MEDIUM) — Array, Depth-First Search, Breadth-First Search, Union Find, Matrix
• Trapping Rain Water II (HARD) — Array, Breadth-First Search, Heap (Priority Queue), Matrix
• Regular Expression Matching (HARD) — String, Dynamic Programming, Recursion
• Kth Smallest Element in a Sorted Matrix (MEDIUM) — Array, Binary Search, Sorting, Heap (Priority Queue), Matrix
• Integer to Roman (MEDIUM) — Hash Table, Math, String
• Valid Parentheses (EASY) — String, Stack
• Merge k Sorted Lists (HARD) — Linked List, Divide and Conquer, Heap (Priority Queue), Merge Sort
• Multiply Strings (MEDIUM) — Math, String, Simulation
• Wildcard Matching (HARD) — String, Dynamic Programming, Greedy, Recursion
• Permutation Sequence (HARD) — Math, Recursion
• Pascal's Triangle (EASY) — Array, Dynamic Programming
• Word Break II (HARD) — Array, Hash Table, String, Dynamic Programming, Backtracking, Trie, Memoization
• Time Needed to Buy Tickets (EASY) — Array, Queue, Simulation
• Max Points on a Line (HARD) — Array, Hash Table, Math, Geometry
• One Edit Distance (MEDIUM) — Two Pointers, String
• Happy Number (EASY) — Hash Table, Math, Two Pointers
• Reverse Linked List (EASY) — Linked List, Recursion
• The Skyline Problem (HARD) — Array, Divide and Conquer, Binary Indexed Tree, Segment Tree, Line Sweep, Heap (Priority Queue), Ordered Set
• Lowest Common Ancestor of a Binary Search Tree (MEDIUM) — Tree, Depth-First Search, Binary Search Tree, Binary Tree
• Flatten 2D Vector (MEDIUM) — Array, Two Pointers, Design, Iterator
• Alien Dictionary (HARD) — Array, String, Depth-First Search, Breadth-First Search, Graph, Topological Sort
• Design Skiplist (HARD) — Linked List, Design
• Number of Connected Components in an Undirected Graph (MEDIUM) — Depth-First Search, Breadth-First Search, Union Find, Graph
• Random Pick with Weight (MEDIUM) — Array, Math, Binary Search, Prefix Sum, Randomized