Medium Coding Problems

Practice 71 medium coding problems on Code Arena — each with a live judge, worked examples, and a solution editorial.

• Greatest Common Divisor — Medium · Math, Number Theory
• Primality Test — Medium · Number Theory, Math
• Maximum Subarray Sum — Medium · Dynamic Programming, Arrays
• Balanced Brackets — Medium · Stack, Strings
• Nth Fibonacci — Medium · Dynamic Programming, Math
• Second Largest — Medium · Arrays
• Count Primes — Medium · Number Theory
• Palindrome Check — Medium · Strings
• Anagram Check — Medium · Strings, Sorting
• GCD of an Array — Medium · Math, Number Theory
• Binary to Decimal — Medium · Math, Strings
• Decimal to Binary — Medium · Math
• Modular Exponentiation — Medium · Math, Number Theory
• Sum of Divisors — Medium · Math, Number Theory
• Count Set Bits — Medium · Math, Bit Manipulation
• Reverse Integer — Medium · Math
• Two Sum Exists — Medium · Arrays, Hashing
• Missing Number — Medium · Arrays, Math
• Kth Largest Element — Medium · Sorting, Arrays
• Most Frequent Element — Medium · Hashing, Arrays
• Single Number — Medium · Bit Manipulation, Arrays
• Majority Element — Medium · Arrays, Algorithms
• Roman to Integer — Medium · Strings, Implementation
• Valid Palindrome — Medium · Strings, Two Pointers
• Search Insert Position — Medium · Binary Search, Arrays
• Climbing Stairs — Medium · Dynamic Programming
• Valid Parentheses — Medium · Stack, Strings
• Most Common Word — Medium · Hashing, Strings
• Parse a Timestamp — Medium · Strings, Implementation
• Format a Video Length — Medium · Math, Implementation
• Cash Register Change — Medium · Greedy, Math
• Caesar Cipher — Medium · Strings, Implementation
• Run-Length Encoding — Medium · Strings
• Credit Card Validation — Medium · Math, Implementation
• Leaderboard Ranking — Medium · Sorting
• Transpose a Grid — Medium · Arrays, Implementation
• Shopping on a Budget — Medium · Greedy, Sorting
• Double-Booked? — Medium · Sorting, Greedy
• IP Address to Integer — Medium · Strings, Math
• Grade Distribution — Medium · Arrays
• Longest Win Streak — Medium · Strings
• Sum a Spreadsheet Column — Medium · Strings, Implementation
• Maximum Nesting Depth — Medium · Stack, Strings
• URL Slug — Medium · Strings, Implementation
• Overtime Pay — Medium · Math, Implementation
• Split the Bill — Medium · Math
• Median Value — Medium · Sorting, Arrays
• Most Common Value — Medium · Arrays, Hashing
• Shift Duration — Medium · Implementation, Math
• Election Winner — Medium · Strings, Hashing
• Password Strength — Medium · Strings, Implementation
• Collatz Steps — Medium · Math, Implementation
• Count Pairs with Sum — Medium · Arrays, Hashing
• Longest Equal Run — Medium · Arrays
• Rotate Array Right — Medium · Arrays, Implementation
• Heaviest Row — Medium · Matrix, Arrays
• Count Anagram Groups — Medium · Strings, Hashing, Sorting
• Two Sum (Sorted) — Medium · Two Pointers, Arrays
• Binary Search — Medium · Binary Search
• Maximum Window Sum — Medium · Sliding Window, Arrays
• Count Distinct (Sorted) — Medium · Two Pointers, Arrays
• Next Greater Element — Medium · Stack, Arrays
• Run-Length Decode — Medium · Strings, Implementation
• Count Pairs With Difference — Medium · Hashing, Arrays
• Subarray With Target Sum — Medium · Sliding Window, Two Pointers, Prefix Sum
• Rotate Matrix 90° — Medium · Matrix, Implementation
• Spiral Order — Medium · Matrix, Implementation
• Pascal's Triangle Row — Medium · Combinatorics, Math
• Power of Two — Medium · Bit Manipulation, Math
• Longest Substring Without Repeats — Medium · Sliding Window, Hashing, Strings
• LCM of Array — Medium · Number Theory, Math

← All problems