Practice Problems

Browse Code Arena's problem bank of classic interview questions and algorithm challenges.

• Sum of Two — Easy
• Greeting — Easy
• Reverse a String — Easy
• FizzBuzz — Easy
• Count the Vowels — Easy
• Sort the Array — Easy
• Greatest Common Divisor — Medium
• Primality Test — Medium
• Maximum Subarray Sum — Medium
• Balanced Brackets — Medium
• Edit Distance — Hard
• Coin Change — Hard
• Array Sum — Easy
• Max of Three — Easy
• Even or Odd — Easy
• Count Words — Easy
• Sum of Digits — Easy
• Factorial — Easy
• Nth Fibonacci — Medium
• Second Largest — Medium
• Count Primes — Medium
• Palindrome Check — Medium
• Anagram Check — Medium
• GCD of an Array — Medium
• Longest Common Subsequence — Hard
• Longest Increasing Subsequence — Hard
• 0/1 Knapsack — Hard
• Minimum of an Array — Easy
• Multiply Two — Easy
• Absolute Value — Easy
• Last Digit — Easy
• To Uppercase — Easy
• Leap Year — Easy
• Count Even Numbers — Easy
• Sum of a Range — Easy
• Character Count — Easy
• Binary to Decimal — Medium
• Decimal to Binary — Medium
• Modular Exponentiation — Medium
• Sum of Divisors — Medium
• Count Set Bits — Medium
• Reverse Integer — Medium
• Two Sum Exists — Medium
• Missing Number — Medium
• Kth Largest Element — Medium
• Most Frequent Element — Medium
• Subset Sum — Hard
• House Robber — Hard
• Unique Grid Paths — Hard
• Longest Palindromic Substring — Hard
• Maximum Product Subarray — Hard
• Nth Prime — Hard
• Two Sum — Easy
• Best Time to Buy and Sell Stock — Easy
• Contains Duplicate — Easy
• Move Zeroes — Easy
• Single Number — Medium
• Majority Element — Medium
• Roman to Integer — Medium
• Valid Palindrome — Medium
• Plus One — Easy
• Search Insert Position — Medium
• Product of Array Except Self — Hard
• Climbing Stairs — Medium
• Merge Two Sorted Arrays — Easy
• Valid Parentheses — Medium
• Length of Last Word — Easy
• Shopping Cart Total — Easy
• Apply a Discount — Easy
• Add Sales Tax — Easy
• Passing Students — Easy
• Class Average — Easy
• Temperature Swing — Easy
• Low Stock Alert — Easy
• Pagination — Easy
• Unique Visitors — Easy
• DNA Mutations — Easy
• GC Content — Easy
• Most Common Word — Medium
• Distinct Words — Easy
• Parse a Timestamp — Medium
• Format a Video Length — Medium
• Cash Register Change — Medium
• Caesar Cipher — Medium
• Run-Length Encoding — Medium
• Credit Card Validation — Medium
• Leaderboard Ranking — Medium
• Transpose a Grid — Medium
• Shopping on a Budget — Medium
• Double-Booked? — Medium
• Minimum Meeting Rooms — Hard
• IP Address to Integer — Medium
• Grade Distribution — Medium
• Longest Win Streak — Medium
• Sum a Spreadsheet Column — Medium
• Maximum Nesting Depth — Medium
• Spend and Save — Easy