String manipulation is one of the most important topics in coding interviews. From reversing strings to solving dynamic programming-based
problems like Edit Distance, mastering string algorithms helps you stand out in technical rounds at companies like Google, Amazon,
Microsoft and Meta.
This guide covers 50 of the most frequently asked string problems, categorized by difficulty level (Easy, Medium, and Hard)
each with a short description, core concepts and key ideas to help you prepare smarter.
Easy Level String Problems
1. Reverse String
Description: Reverse the characters of a given string in-place. Concepts: Two-pointer swap, in-place modification. Example: Input: "hello" -> Output: "olleh"
2. Reverse Words in a String
Description: Reverse the order of words in a sentence without altering characters in each word. Concepts: Splitting, trimming spaces, joining with reversed order.
3. Check Palindrome String
Description: Determine whether a string reads the same backward as forward. Concepts: Two-pointer technique, character comparison.
4. Valid Anagram
Description: Check if two strings contain the same characters with the same frequencies. Concepts: Sorting, frequency counting (HashMap). Example:"anagram" vs "nagaram" -> true
5. First Unique Character in a String
Description: Find the index of the first non-repeating character. Concepts: HashMap frequency counting, linear scan.
6. Remove All Adjacent Duplicates
Description: Continuously remove adjacent repeating characters until no duplicates remain. Concepts: Stack-based removal approach.
7. Implement strStr()
Description: Return the index of the first occurrence of a substring (needle) in another string (haystack). Concepts: Brute force, KMP (Knuth-Morris-Pratt) algorithm.
8. Longest Common Prefix
Description: Find the longest common prefix string among an array of strings. Concepts: Sorting, character-by-character comparison.
9. Count Vowels and Consonants
Description: Count the number of vowels and consonants in a string. Concepts: Iteration, set lookup.
10. Check if String is Rotation of Another
Description: Determine if one string can be obtained by rotating another. Concepts: Concatenation trick (s1 + s1 contains s2).
11. Check if String is Subsequence of Another
Description: Check whether string s is a subsequence of string t. Concepts: Two-pointer traversal.
12. Convert String to Integer (atoi)
Description: Parse a numeric string into an integer while handling spaces, signs, and overflow. Concepts: Parsing logic, overflow handling.
13. Check Balanced Parentheses
Description: Verify if the parentheses/brackets in a string are balanced. Concepts: Stack push/pop validation.
14. Find All Permutations of a String
Description: Generate all unique permutations of a given string. Concepts: Backtracking recursion.
15. Check Isomorphic Strings
Description: Check if two strings have the same pattern of character mapping. Concepts: Hash mapping for pattern consistency.
Medium Level String Problems
16. Group Anagrams
Description: Group together all strings that are anagrams of each other. Concepts: Sorting character signature, HashMap grouping.
17. Longest Substring Without Repeating Characters
Description: Find the length of the longest substring without duplicate characters. Concepts: Sliding window with character frequency map.
18. Longest Palindromic Substring
Description: Find the longest substring that is a palindrome. Concepts: Expand around center, dynamic programming.
19. Minimum Window Substring
Description: Find the smallest substring containing all characters of another string. Concepts: Sliding window, frequency counting.
20. Valid Parentheses String with *
Description: Check if a string with (, ) and * can be valid. Concepts: Greedy approach, range tracking.
String manipulation is one of the most important topics in coding interviews. From reversing strings to solving dynamic programming-based\nproblems like Edit Distance, mastering string algorithms helps you stand out in technical rounds at companies like Google, Amazon,\nMicrosoft and Meta.
\n
This guide covers 50 of the most frequently asked string problems, categorized by difficulty level (Easy, Medium, and Hard)\neach with a short description, core concepts and key ideas to help you prepare smarter.
\n
Easy Level String Problems
\n
1. Reverse String
\n
Description: Reverse the characters of a given string in-place. \nConcepts: Two-pointer swap, in-place modification. \nExample: Input: \"hello\" -> Output: \"olleh\"
\n
2. Reverse Words in a String
\n
Description: Reverse the order of words in a sentence without altering characters in each word. \nConcepts: Splitting, trimming spaces, joining with reversed order.
\n
3. Check Palindrome String
\n
Description: Determine whether a string reads the same backward as forward. \nConcepts: Two-pointer technique, character comparison.
\n
4. Valid Anagram
\n
Description: Check if two strings contain the same characters with the same frequencies. \nConcepts: Sorting, frequency counting (HashMap). \nExample:\"anagram\" vs \"nagaram\" -> true
\n
5. First Unique Character in a String
\n
Description: Find the index of the first non-repeating character. \nConcepts: HashMap frequency counting, linear scan.
\n
6. Remove All Adjacent Duplicates
\n
Description: Continuously remove adjacent repeating characters until no duplicates remain. \nConcepts: Stack-based removal approach.
\n
7. Implement strStr()
\n
Description: Return the index of the first occurrence of a substring (needle) in another string (haystack). \nConcepts: Brute force, KMP (Knuth-Morris-Pratt) algorithm.
\n
8. Longest Common Prefix
\n
Description: Find the longest common prefix string among an array of strings. \nConcepts: Sorting, character-by-character comparison.
\n
9. Count Vowels and Consonants
\n
Description: Count the number of vowels and consonants in a string. \nConcepts: Iteration, set lookup.
\n
10. Check if String is Rotation of Another
\n
Description: Determine if one string can be obtained by rotating another. \nConcepts: Concatenation trick (s1 + s1 contains s2).
\n
11. Check if String is Subsequence of Another
\n
Description: Check whether string s is a subsequence of string t. \nConcepts: Two-pointer traversal.
\n
12. Convert String to Integer (atoi)
\n
Description: Parse a numeric string into an integer while handling spaces, signs, and overflow. \nConcepts: Parsing logic, overflow handling.
\n
13. Check Balanced Parentheses
\n
Description: Verify if the parentheses/brackets in a string are balanced. \nConcepts: Stack push/pop validation.
\n
14. Find All Permutations of a String
\n
Description: Generate all unique permutations of a given string. \nConcepts: Backtracking recursion.
\n
15. Check Isomorphic Strings
\n
Description: Check if two strings have the same pattern of character mapping. \nConcepts: Hash mapping for pattern consistency.
\n
Medium Level String Problems
\n
16. Group Anagrams
\n
Description: Group together all strings that are anagrams of each other. \nConcepts: Sorting character signature, HashMap grouping.
\n
17. Longest Substring Without Repeating Characters
\n
Description: Find the length of the longest substring without duplicate characters. \nConcepts: Sliding window with character frequency map.
\n
18. Longest Palindromic Substring
\n
Description: Find the longest substring that is a palindrome. \nConcepts: Expand around center, dynamic programming.
\n
19. Minimum Window Substring
\n
Description: Find the smallest substring containing all characters of another string. \nConcepts: Sliding window, frequency counting.
\n
20. Valid Parentheses String with *
\n
Description: Check if a string with (, ) and * can be valid. \nConcepts: Greedy approach, range tracking.
Boost your confidence for Top Tech Companies Interview like FAANG-level interviews
\n
","categoryId":177,"subCategoryId":177,"contentFormat":5,"blogId":26,"userId":"MjlfNF84LVs0XTJuLXRDX0FOZ2VfX0l0","title":"Top 50 Most Frequently Asked String Coding Problems (Interview Preparation )","url":"top-50-most-frequently-asked-string-coding-problems-interview-preparation","bannerImage":"","seoDescription":"","generatedOn":"2025-10-05T07:41:13","updatedOn":"2025-10-05T07:41:13"},"popularContents":[{"id":171,"title":"Meesho SDE-1 Backend Interview Experience (Remote | 3 Round) - Rejected","url":"meesho-sde-1-backend-interview-experience-remote-3-round-rejected","description":null,"seoDescription":"Read a real Meesho SDE-1 Backend interview experience covering the online assessment, DSA interview, machine coding round, LLD questions and preparation tips.","contentType":5,"generatedOn":"2026-10-14T22:53:55.9912329Z","viewCount":0},{"id":167,"title":"Meesho SDE-1 Online Assessment Interview Experience (Remote) - Rejected","url":"meesho-sde-1-online-assessment-interview-experience-remote-rejected","description":null,"seoDescription":"Read a real Meesho SDE-1 online assessment experience with coding questions, DSA topics, solutions, difficulty level, preparation tips and interview insights.","contentType":5,"generatedOn":"2026-10-14T22:53:55.9912311Z","viewCount":0},{"id":83,"title":"Uber SDE 2 Interview Experience (5 Rounds, Selected) - Complete DSA Questions with solution, System Design & Managerial Round","url":"uber-sde-2-interview-experience","description":null,"seoDescription":"Uber SDE 2 interview experience with 5 rounds, real DSA questions, system design, coding round, and preparation tips to crack Uber interviews.","contentType":5,"generatedOn":"2026-10-14T22:53:55.9912275Z","viewCount":0},{"id":213,"title":"Amazon SDE II Interview Experience (Bangalore, Selected) ~ Aug 2026","url":"amazon-sde-ii-interview-experience-bangalore-selected-aug-2026","description":null,"seoDescription":"Amazon SDE II interview experience from Bangalore covering 4 rounds, DSA, LLD, system design, Leadership Principles, coding questions and selection.","contentType":5,"generatedOn":"2026-10-14T22:53:55.991238Z","viewCount":0},{"id":197,"title":"My Adobe SDE Interview Experience (Aug 2026) 5 Rounds, Selected","url":"my-adobe-sde-interview-experience-aug-2026-5-rounds-selected","description":null,"seoDescription":"Real Adobe SDE interview: 5 rounds, 4 DSA problems (Rotate Array, BSTs, Kth Smallest Matrix), code review & behavioral round. Full solutions + tips.","contentType":5,"generatedOn":"2026-10-14T22:53:55.9912364Z","viewCount":0},{"id":135,"title":"Spinny SDE-1 Interview Experience (Selected)","url":"spinny-sde-1-interview-experience-selected","description":null,"seoDescription":"Spinny SDE-1 Interview Experience (Selected) | 4 Rounds Breakdown: Coding, LLD, Java, SQL + Real Interview Questions","contentType":5,"generatedOn":"2026-10-14T22:53:55.9912295Z","viewCount":0},{"id":173,"title":"Uber SDE-2 Interview Experience : LLD, HLD, DSA & Hiring Manager Round","url":"uber-sde-2-interview-experience-lld-hld-dsa-hiring-manager-round","description":null,"seoDescription":"Read a real Uber SDE-2 interview experience covering DSA, low-level design, high-level system design, behavioral rounds, hiring freeze and key takeaways.","contentType":5,"generatedOn":"2026-10-14T22:53:55.9912346Z","viewCount":0},{"id":165,"title":"Top 50+ SQL Interview Questions and Answers for Intermediate to Advanced","url":"top-sql-interview-questions-and-answers-for-intermediate-to-advanced","description":null,"seoDescription":"Top SQL Interview Questions and Answers for Intermediate to Advanced. Top SQL Interview Questions for experience. Frequently asked SQL interview questions with answers","contentType":2,"generatedOn":"2026-10-14T22:53:55.9899635Z","viewCount":0},{"id":35,"title":"Cursor vs Copilot : Which AI Coding Assistant Wins in 2025?","url":"cursor-vs-copilot-which-ai-coding-assistant-truly-wins-in-2025","description":null,"seoDescription":"Compare Cursor vs GitHub Copilot on speed, context awareness, multi-file support, pricing and code quality to choose the best AI coding assistant for developers","contentType":5,"generatedOn":"2026-10-14T22:53:55.9912248Z","viewCount":0},{"id":163,"title":"Top 50 SQL Interview Questions and Answers (Beginner to Intermediate)","url":"top-sql-interview-questions-and-answers-beginner-to-intermediate","description":null,"seoDescription":"Top 50 SQL Interview Questions and Answers (Beginner to Intermediate). Top SQL Interview Questions for fresher. Frequently asked SQL interview questions with answers","contentType":2,"generatedOn":"2026-10-14T22:53:55.9899581Z","viewCount":0}],"latestContents":[{"id":219,"title":"6 Tools That Made My Life Easier as a Software Engineer","url":"6-tools-that-made-my-life-easier-as-a-software-engineer","description":null,"seoDescription":"The 6 developer tools I use daily as a software engineer: Git, VS Code, Docker, Postman, Chrome DevTools, and AI assistants, with real tips, mistakes, and trade","contentType":5,"generatedOn":"2026-10-14T22:53:55.9911469Z","viewCount":0},{"id":218,"title":"When Should a Business Use Multiple AI Agents Instead of One?","url":"when-should-a-business-use-multiple-ai-agents-instead-of-one","description":null,"seoDescription":"Single agent or multi-agent AI? Learn the 4 signals that justify splitting agents by knowledge, permissions, and risk, plus routing and handoff tips.","contentType":5,"generatedOn":"2026-10-14T22:53:55.9911515Z","viewCount":0},{"id":216,"title":"AI in Clinical Trials Market Estimated to Experience a Hike in Growth by 2035","url":"ai-in-clinical-trials-market-estimated-to-experience-a-hike-in-growth-by-2035","description":null,"seoDescription":"The exclusive information about market dynamics serves as a valuable guide to predict economic scenarios and initiatives taken to enhance future growth. Our mar","contentType":5,"generatedOn":"2026-10-14T22:53:55.9911533Z","viewCount":0},{"id":217,"title":"AI in Clinical Trials Market Estimated to Experience a Hike in Growth by 2035","url":"ai-in-clinical-trials-market-estimated-to-experience-a-hike-in-growth-by-2035","description":null,"seoDescription":"The exclusive information about market dynamics serves as a valuable guide to predict economic scenarios and initiatives taken to enhance future growth. Our mar","contentType":5,"generatedOn":"2026-10-14T22:53:55.9911581Z","viewCount":0},{"id":215,"title":"What Happens When an AI Agent Doesn't Know the Answer?","url":"what-happens-when-an-ai-agent-doesnt-know-the-answer","description":null,"seoDescription":"Most AI agents fail quietly. They guess instead of saying \"I don't know.\" Here's how to design better fallback and human-handoff behavior.","contentType":5,"generatedOn":"2026-10-14T22:53:55.9911595Z","viewCount":0},{"id":214,"title":"Greedy Algorithms Explained: How They Work, When They Fail and How to Use Them","url":"greedy-algorithms-explained-how-they-work-when-they-fail-and-how-to-use-them","description":null,"seoDescription":"Learn greedy algorithms step by step with C# code Dijkstra, Huffman coding, knapsack and MSTs plus when greedy fails and how to prove it's correct","contentType":5,"generatedOn":"2026-10-14T22:53:55.9911612Z","viewCount":0},{"id":213,"title":"Amazon SDE II Interview Experience (Bangalore, Selected) ~ Aug 2026","url":"amazon-sde-ii-interview-experience-bangalore-selected-aug-2026","description":null,"seoDescription":"Amazon SDE II interview experience from Bangalore covering 4 rounds, DSA, LLD, system design, Leadership Principles, coding questions and selection.","contentType":5,"generatedOn":"2026-10-14T22:53:55.9911625Z","viewCount":0},{"id":212,"title":"How to Get 10x Better AI Answers Without Writing Better Prompts : 10 Proven Techniques","url":"how-to-get-10x-better-ai-answers-without-writing-better-prompts-10-proven-techniques","description":null,"seoDescription":"Get better AI answers without complex prompts. Learn 10 practical techniques using context, examples, tools, feedback, and verification.","contentType":5,"generatedOn":"2026-10-14T22:53:55.9911639Z","viewCount":0},{"id":211,"title":"I Interviewed for a Microsoft SDE I Role. Here's Everything That Happened.","url":"i-interviewed-for-a-microsoft-sde-i-role-heres-everything-that-happened","description":null,"seoDescription":"My real Microsoft SDE I interview experience, all 4 rounds, the exact DSA problems with fully tested solutions, the WhatsApp system design round","contentType":5,"generatedOn":"2026-10-14T22:53:55.9911654Z","viewCount":0},{"id":140,"title":"PolicyBazaar Software Development Engineer (SDE) Interview Experience | DSA, Core CS & System Design","url":"policybazaar-software-development-engineer-sde-interview-experience-dsa-core-cs-system-design","description":null,"seoDescription":"Detailed PolicyBazaar SDE interview experience covering 3 rounds: DSA coding, core CS assessment and system design with key learnings and insights.","contentType":5,"generatedOn":"2026-10-14T22:53:55.9911668Z","viewCount":0}],"relatedContents":[{"id":207,"title":"How to Find the Right View of a Binary Tree","url":"right-view-of-a-binary-tree","description":null,"seoDescription":"Learn how to find the right view of a binary tree using DFS and BFS, with examples, code, complexity analysis and coding interview tips.","contentType":5,"generatedOn":"2026-10-14T22:53:55.9949766Z","viewCount":0},{"id":206,"title":"Left View of a Binary Tree: DFS and BFS Approaches Explained","url":"left-view-of-a-binary-tree","description":null,"seoDescription":"Learn how to find the left view of a binary tree using DFS and BFS, with examples, code, complexity analysis, common mistakes and interview tips.","contentType":5,"generatedOn":"2026-10-14T22:53:55.9949797Z","viewCount":0},{"id":205,"title":"Top View of a Binary Tree Using BFS and DFS | Complete Guide","url":"top-view-of-a-binary-tree","description":null,"seoDescription":"Learn how to find the top view of a binary tree using DFS and BFS with step-by-step explanations, examples, code, complexity analysis and interview insights.","contentType":5,"generatedOn":"2026-10-14T22:53:55.9949813Z","viewCount":0},{"id":201,"title":"Bottom View of a Binary Tree: DFS vs BFS Approach","url":"bottom-view-of-a-binary-tree-dfs-vs-bfs-approach","description":null,"seoDescription":"Learn to find the bottom view of a binary tree using horizontal distance. Compares a buggy DFS attempt, a fixed DFS and the optimal BFS solution in Java.","contentType":5,"generatedOn":"2026-10-14T22:53:55.9949826Z","viewCount":0},{"id":200,"title":" Longest Playlist With No Repeated Songs : Brute Force to Optimal","url":"longest-playlist-with-no-repeated-songs-brute-force-to-optimal","description":null,"seoDescription":"Find the longest playlist with no repeated songs using brute force, HashSet, and HashMap sliding window techniques, with Java code and dry runs.","contentType":5,"generatedOn":"2026-10-14T22:53:55.994984Z","viewCount":0},{"id":90,"title":"Contain Virus : Deep, Intuitive & Fully Explained Guide","url":"contain-virus-deep-intuitive-fully-explained-guide","description":null,"seoDescription":"Contain Virus problem explained with DFS + greedy approach, step-by-step simulation, examples and optimized solutions for coding interviews.","contentType":5,"generatedOn":"2026-10-14T22:53:55.9949856Z","viewCount":0},{"id":37,"title":"Find the repeating and missing numbers","url":"find-the-repeating-and-missing-numbers","description":null,"seoDescription":"Find the repeating and missing numbers in an array from 1..n using brute force, hashmap, math and XOR, step-by-step explained with real-world use cases.","contentType":5,"generatedOn":"2026-10-14T22:53:55.994987Z","viewCount":0},{"id":27,"title":"4 Sum | Find Quads that add up to a target value","url":"4-sum-find-quads-that-add-up-to-a-target-value","description":null,"seoDescription":"","contentType":5,"generatedOn":"2026-10-14T22:53:55.9949904Z","viewCount":0},{"id":25,"title":"Intersection of Two Sorted Arrays","url":"intersection-of-two-sorted-arrays","description":null,"seoDescription":"","contentType":5,"generatedOn":"2026-10-14T22:53:55.9949934Z","viewCount":0}]}}},"source":{"isMobile":false}};
window.__CLIENT_RENDER__ = false;
![\"Amazon](\"https://m.media-amazon.com/images/G/31/img17/AmazonPay/Aditya_Vangala/Main-Page_PC_01_KSD.jpg\")
\n