# Problems by Difficulty Source: https://www.techinterview.org/problems-by-difficulty/ Updated: 2026-07-02 ยท techinterview.org Problems by Difficulty Choose problems based on your skill level and interview preparation stage. ## How to Use This Index - **Beginners (0-1 years):** Start with Easy-Medium problems - **Intermediate (2-4 years):** Focus on Medium problems - **Advanced (5+ years):** Master Hard problems for senior roles ## Easy-Medium Problems (5) **Best for:** Interview preparation fundamentals, building confidence, learning basic patterns. **Time to solve:** 20-35 minutes - [Check if a Linked list is a Palindrome or Not](https://www.techinterview.org/post/3233459641/check-if-a-linked-list-is-a-palindrome-or-not/) - [Find Longest Palindrome In A String](https://www.techinterview.org/post/3233459618/find-longest-palindrome-in-a-string/) - [Palindromes](https://www.techinterview.org/post/526332105/palindromes/) - [Reverse a doubly linked list](https://www.techinterview.org/post/3233459635/reverse-a-doubly-linked-list/) - [Reverse a String](https://www.techinterview.org/post/526374214/reverse-a-string/) ## Medium Problems (49) **Best for:** Most technical interviews at top companies. This is the sweet spot. **Time to solve:** 30-45 minutes **Companies:** Google, Amazon, Facebook, Microsoft, Apple all ask Medium problems. - [100 Factorial](https://www.techinterview.org/post/491337394/100-factorial/) - [Amazon Interview Question: Count Negative Integers in Matrix](https://www.techinterview.org/post/3233459698/amazon-interview-question-count-negative-integers-in-matrix/) - [Bit Manipulation: Essential Tricks and Techniques](/post/3233460816/bit-manipulation-interview-patterns/) - [Boolean String Value](https://www.techinterview.org/post/3233459765/boolean-string-value/) - [Box 'o Numbers](https://www.techinterview.org/post/489558891/box-o-numbers/) - [Building a Stack with a getMax() function](https://www.techinterview.org/post/3233459129/building-a-stack-with-a-getmax-function/) - [Bumblebee](https://www.techinterview.org/post/526342692/bumblebee/) - [Card Trick Without the Trick](https://www.techinterview.org/post/526296398/card-trick-without-the-trick/) - [Check If a Number is Power of Two](https://www.techinterview.org/post/3233459629/check-if-a-number-is-power-of-two/) - [Chessboard](https://www.techinterview.org/post/526280776/chessboard/) - [Classic Weighing](https://www.techinterview.org/post/523914909/classic-weighing/) - [Clock](https://www.techinterview.org/post/521425053/clock/) - [Coin Rolls](https://www.techinterview.org/post/508833401/coin-rolls/) - [Compute X^Y For Floats and Negative Values](https://www.techinterview.org/post/3233459637/compute-xy-for-floats-and-negative-values/) - [Cube](https://www.techinterview.org/post/518750698/cube/) - [Find Out if a Linked List has a Cycle](https://www.techinterview.org/post/3233459674/find-out-if-a-linked-list-has-a-cycle/) - [Find The Depth of a Binary Tree](https://www.techinterview.org/post/3233459627/find-the-depth-of-a-binary-tree/) - [Fruit Jar Problem](https://www.techinterview.org/post/3233459687/fruit-jar-problem/) - [Function that Multiples 2 Integers](https://www.techinterview.org/post/3233459676/function-that-multiples-2-integers/) - [Fuse on Fire](https://www.techinterview.org/post/526289631/fuse-on-fire/) - [Getting a fair result with an unfair coin](https://www.techinterview.org/post/3233458616/getting-a-fair-result-with-an-unfair-coin/) - [Gold Chain](https://www.techinterview.org/post/521433747/gold-chain/) - [How many floors can an egg be dropped without breaking?](https://www.techinterview.org/post/3233459133/dropping-an-egg/) - [Implement a Function to Return a Ratio](https://www.techinterview.org/post/3233459671/implement-a-function-to-return-a-ratio/) - [Implement a rate limiter](https://www.techinterview.org/post/3233459770/implement-a-rate-limiter/) - [Implement LRU Cache](/post/3233472889/lld-lru-cache/) - [Implement Trie (Prefix Tree)](/post/3233466827/trie-patterns/) - [int atoi( char* pStr )](https://www.techinterview.org/post/526339864/int-atoi-char-pstr/) - [Kadane's Algorithm: Maximum Subarray Sum](/post/3233466767/array-advanced-patterns/) - [Linked List](https://www.techinterview.org/post/3233466900/linked-list-patterns/) - [Missing country code](https://www.techinterview.org/post/3233459746/missing-country-code/) - [Missing or Duplicate Number in an Array](https://www.techinterview.org/post/3233459624/missing-or-duplicate-number-in-an-array/) - [Monty Hall Problem](https://www.techinterview.org/post/523909089/monty-hall-problem/) - [Prime number problem](https://www.techinterview.org/post/3233459742/prime-number-problem-2/) - [Print String Permutations](https://www.techinterview.org/post/3233459701/print-string-permutations/) - [Probability Distribution Function](https://www.techinterview.org/post/3233459639/probability-distribution-function/) - [Red Marbles, Blue Marbles](https://www.techinterview.org/post/526363745/red-marbles-blue-marbles/) - [Removing a Character from a String](https://www.techinterview.org/post/3233459622/removing-a-character-from-a-string/) - [Right Rotate an array by k elements](https://www.techinterview.org/post/3233459583/right-rotate-an-array-by-k-elements/) - [Server to Process Fair Number of Functions](https://www.techinterview.org/post/3233459683/server-to-process-fair-number-of-functions/) - [Sliding Window Maximum](/post/3233466720/priority-queue-patterns/) - [Storing 1 million phone numbers](https://www.techinterview.org/post/1731330243/storing-1-million-phone-numbers/) - [Sum it Up](https://www.techinterview.org/post/526329049/sum-it-up/) - [Sum Up a Pair in Array](https://www.techinterview.org/post/3233459633/sum-up-a-pair-in-array/) - [Topological Sort](/post/3233461698/topological-sort-interview-patterns/) - [Treasure Island](https://www.techinterview.org/post/521415913/treasure-island/) - [Write a Function for r and 5()](https://www.techinterview.org/post/3233459678/write-a-function-for-r-and-5/) - [Write a program for producer-consumer problem](https://www.techinterview.org/post/3233459644/write-a-program-for-producer-consumer-problem/) - [XOR using NAND gates](https://www.techinterview.org/post/489166573/xor-using-nand-gates/) ## Hard Problems (5) **Best for:** Senior/Staff engineer roles, demonstrating advanced problem-solving. **Time to solve:** 45-60 minutes **Companies:** Google L5+, Facebook E5+, Microsoft 64+ often include Hard problems. - [Dijkstra's Shortest Path Algorithm](/post/3233463789/shortest-path-algorithm-patterns/) - [Hard River Crossing](https://www.techinterview.org/post/523919913/hard-river-crossing/) - [Serialize and Deserialize a Binary Tree](https://www.techinterview.org/post/3233459646/serialize-and-deserialize-a-binary-tree/) - [Union-Find (Disjoint Set Union)](/post/3233464033/union-find-dsu-interview-patterns/) - [Word Search in Grid](/post/3233465934/trie-advanced-interview-patterns/)