A curated set of 50 high-frequency, representative interview problems. This list is optimized for practical prep value: the questions people are most likely to see, remember, and benefit from repeating.


Two Sum

Contains Duplicate

Teaches single-pass running-minimum scanning.

Best Time to Buy and Sell Stock

Covers hash-map grouping by a canonical key.

Group Anagrams

Covers frequency counting with ranked selection.

Top K Frequent Elements

Longest Consecutive Sequence

Valid Palindrome

Two pointers with a non-obvious pruning argument.

Container With Most Water

Extends two-pointer search after sorting.

3Sum

Challenges with a hard two-pointer variant.

Trapping Rain Water

Longest Substring Without Repeating Characters

Extends sliding window with a replacement budget.

Longest Repeating Character Replacement

Hardens sliding-window with shrink conditions.

Minimum Window Substring

Valid Parentheses

Min Stack

Daily Temperatures

Binary Search

Find Minimum in Rotated Sorted Array

Applies rotated binary search to lookups.

Search in Rotated Sorted Array

Reverse Linked List

Covers the core linked-list merge pattern.

Merge Two Sorted Lists

Introduces fast/slow-pointer cycle detection.

Linked List Cycle

Remove Nth Node From End of List

Introduces interval-merge after sorting by start.

Merge Intervals

Insert Interval

Non-overlapping Intervals

Same Tree

Maximum Depth of Binary Tree

Invert Binary Tree

Binary Tree Level Order Traversal

Validate Binary Search Tree

Uses BST in-order traversal for ordering.

Kth Smallest Element in a BST

Lowest Common Ancestor of a Binary Tree

Introduces grid DFS/BFS for connected components.

Number of Islands

Covers graph traversal with cycle handling.

Clone Graph

Graph Valid Tree

Introduces topological sort and cycle detection.

Course Schedule

Pacific Atlantic Water Flow

Word Ladder

K Closest Points to Origin

Merge K Sorted Lists

Find Median from Data Stream

Combination Sum

Word Search

Pushes backtracking with constraint pruning.

N-Queens

Climbing Stairs

Introduces 1D DP with take-or-skip choices.

House Robber

Coin Change

Word Break

Longest Increasing Subsequence

Monster 50

Blind 75 is the go-to list for interview prep, but most platforms make you tackle it alone. On AlgoMonster, each problem is backed by the core patterns you've already learned, so you're not just guessing — you're applying real techniques. And if you mess up, we'll tell you exactly where you went wrong and how to fix it. It's the Blind 75, but finally with actual support.


This problem tests understanding of string manipulation, dynamic programming, and the ability to optimize solutions from O(n²) to O(n) using Manacher's algorithm.

Longest Palindromic Substring

This problem tests understanding of string manipulation, dynamic programming, and the ability to count all possible palindromic substrings efficiently.

Palindromic Substrings

This problem tests understanding of mathematical properties, bit manipulation, and the ability to find missing elements in a sequence.

Missing Number

Introduces the use of slow-fast pointers, reversing a linked list, and merging two lists.

Reorder List

Introduces Topological Sorting using Kahn's Algorithm (BFS) and DFS for cycle detection in a Directed Acyclic Graph (DAG).

Alien Dictionary

This problem tests understanding of string manipulation, encoding/decoding techniques, and the ability to design algorithms for data serialization.

Encode and Decode Strings

This problem tests understanding of dynamic programming, handling negative numbers, and maintaining both maximum and minimum products to find the optimal solution.

Maximum Product Subarray

This problem tests understanding of tree traversal, serialization formats, and tree reconstruction from a string representation.

Serialize and Deserialize Binary Tree

This problem tests understanding of matrix manipulation, in-place operations, and geometric transformations.

Rotate Image

This problem tests understanding of dynamic programming, subarray optimization, and state transitions. It's a fundamental problem that appears in many interviews and has practical applications in financial analysis.

Maximum Subarray

This problem tests understanding of matrix traversal, boundary conditions, and direction changes. It's a common interview question that requires careful handling of edge cases.

Spiral Matrix

Introduces Greedy algorithms and Dynamic Programming for solving reachability problems.

Jump Game

This problem tests understanding of tree traversal, recursion, and tree comparison. It's a fundamental problem that helps build intuition for more complex tree problems.

Subtree of Another Tree

This problem tests understanding of dynamic programming, combinatorial mathematics, and grid traversal. It's a classic problem that appears frequently in interviews and has practical applications in path planning.

Unique Paths

This problem tests understanding of bit manipulation, binary operations, and number representation. It's a fundamental problem that helps build intuition for more complex bit manipulation problems.

Reverse Bits

This problem tests understanding of bit manipulation, binary operations, and counting techniques. It's a fundamental problem that helps build intuition for more complex bit manipulation problems.

Number of 1 Bits

This problem tests understanding of graph traversal, DFS/BFS, and connected components. It's a fundamental problem that helps build intuition for graph algorithms and component analysis.

Number of Connected Components in an Undirected Graph

This problem tests understanding of matrix manipulation, in-place algorithms, and space optimization. It's a common interview question that requires careful handling of edge cases and space constraints.

Set Matrix Zeroes

Introduces Trie data structures, which are useful for prefix-based searching.

Implement Trie (Prefix Tree)

This problem tests understanding of bit manipulation, dynamic programming, and pattern recognition. It's a fundamental problem that helps build intuition for more complex bit manipulation and dynamic programming problems.

Counting Bits

This problem tests understanding of trie data structures, backtracking, and graph traversal. It's a challenging problem that combines multiple algorithmic concepts and is frequently asked in interviews.

Word Search II

This problem tests understanding of dynamic programming, circular array handling, and state transitions. It's a variation of the classic House Robber problem that adds the complexity of a circular arrangement.

House Robber II

This problem tests understanding of dynamic programming, string manipulation, and state transitions. It's a classic problem that requires careful handling of edge cases and overlapping subproblems.

Decode Ways

This problem tests understanding of intervals, heaps, and sorting. It's a common interview question that requires efficient handling of overlapping intervals.

Meeting Rooms II

This problem tests understanding of dynamic programming, string manipulation, and subsequence problems. It's a classic problem that forms the basis for many more complex string problems.

Longest Common Subsequence

This problem tests understanding of tree traversal, recursion, and array manipulation. It's a fundamental problem that helps build intuition for tree construction and traversal patterns.

Construct Binary Tree from Preorder and Inorder Traversal

Introduces prefix and suffix multiplication techniques for in-place computations.

Product of Array Except Self

This problem tests understanding of bit manipulation, binary arithmetic, and optimization. It's a classic problem that requires thinking about how addition works at the binary level.

Sum of Two Integers

This problem tests understanding of intervals, sorting, and overlap detection. It's a fundamental problem that helps build intuition for more complex interval problems.

Meeting Rooms

This problem tests understanding of tree traversal, dynamic programming on trees, and path finding. It's a challenging problem that requires careful handling of negative values and path constraints.

The highest-ROI interview questions, organized by category.