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
• Tip Total — Easy
• Change Due — Easy
• Seconds to HH:MM:SS — Easy
• Discounted Price — Easy
• Letter Grade — Easy
• Count Uppercase Letters — Easy
• Account Balance — Easy
• RGB to Hex Color — Easy
• Title Case — Easy
• URL Slug — Medium
• Parking Fee — Easy
• Overtime Pay — Medium
• Split the Bill — Medium
• Median Value — Medium
• Most Common Value — Medium
• Shift Duration — Medium
• Election Winner — Medium
• Password Strength — Medium
• Longest Word — Easy
• Product of Digits — Easy
• Collatz Steps — Medium
• Sum of Multiples — Easy
• Count Pairs with Sum — Medium
• Subarrays Summing to K — Hard
• Longest Equal Run — Medium
• Rotate Array Right — Medium
• Heaviest Row — Medium
• Count Anagram Groups — Medium
• Minimum Subset Difference — Hard
• Restock Alert — Easy
• Digital Root — Easy
• Count Negatives — Easy
• Even Numbers Up To N — Easy
• Repeat String — Easy
• Array Range — Easy
• Sum of Even Elements — Easy
• Reverse the Words — Easy
• Count Divisors — Easy
• Running Maximum — Easy
• Hex to Decimal — Easy
• Two Sum (Sorted) — Medium
• Binary Search — Medium
• Maximum Window Sum — Medium
• Count Distinct (Sorted) — Medium
• Next Greater Element — Medium
• Run-Length Decode — Medium
• Count Pairs With Difference — Medium
• Subarray With Target Sum — Medium
• Rotate Matrix 90° — Medium
• Spiral Order — Medium
• Pascal's Triangle Row — Medium
• Power of Two — Medium
• Longest Substring Without Repeats — Medium
• LCM of Array — Medium
• Count Islands — Hard
• Coin Change (Count Ways) — Hard
• Longest Common Substring — Hard
• Minimum Path Sum — Hard
• Word Break — Hard
• Largest Rectangle in Histogram — Hard
• Sum of Squares — Easy
• Count Odd Numbers — Easy
• Minimum and Maximum — Easy
• Alternating Sum — Easy
• Prefix Sums — Easy
• Count Above Average — Easy
• Capitalize Words — Easy
• Trailing Zero Bits — Easy
• Swap Case — Easy
• Add Two Arrays — Easy
• Merge Intervals — Medium
• Count Pairs With Sum — Medium
• Sort Colors — Medium
• Rotate Array Left — Medium
• Valid Mountain Array — Medium
• Search in Rotated Array — Medium
• Next Permutation — Medium
• Sort by Frequency — Medium
• Add Binary Strings — Medium
• Decimal to Hex — Medium
• Matrix Diagonal Sum — Medium
• Jump Game — Medium
• Minimum Size Subarray Sum — Medium
• Reverse in Groups — Medium
• N-Queens Count — Hard
• Shortest Grid Path — Hard
• K-th Permutation — Hard
• Equal Subset Partition — Hard
• Trapping Rain Water — Hard
• Maximal Square — Hard
• Sum of Cubes — Easy
• Count Positive Numbers — Easy
• Floor of Average — Easy
• Second Smallest — Easy
• Palindrome Number — Easy
• Count Digits — Easy
• Interleave Arrays — Easy
• Remove Spaces — Easy
• Max Consecutive Ones — Easy
• Absolute Values — Easy
• Subarrays With Product Below K — Medium
• Longest Consecutive Sequence — Medium
• Find the Duplicate — Medium
• Running Minimum — Medium
• Count Inversions — Medium
• Rotate String — Medium
• K-th Smallest Element — Medium
• Gas Station — Medium
• Container With Most Water — Medium
• Minimum in Rotated Array — Medium
• First Unique Character — Medium
• Subarrays Divisible by K — Medium
• Intersection of Two Arrays — Medium
• Partition Labels — Medium
• Sliding Window Maximum — Hard
• Course Schedule — Hard
• Decode Ways — Hard
• Set Matrix Zeroes — Hard
• Longest Valid Parentheses — Hard
• Max Area of Island — Hard
• XP to Level — Easy
• Typing Speed — Easy
• Traffic Light — Easy
• Seconds to Midnight — Easy
• Dropped Frames — Easy
• Health Bar — Easy
• Tournament Byes — Easy
• Keystroke Count — Easy
• Snake Length — Easy
• First Free Spot — Easy
• Bracket Rounds — Medium
• Rating Simulation — Medium
• Lamp Toggles — Medium
• Matchmaking Gap — Medium
• Loot Split — Medium
• Patrol Coverage — Medium
• Dice Sum Ways — Medium
• Keypad Taps — Medium
• Boustrophedon Seat — Medium
• Digit Sum in Base — Medium
• Compression Sizes — Medium
• Tournament Champion — Medium
• Fit the Most Tasks — Medium
• Staircase With K Steps — Medium
• Minimum Patrol Guards — Hard
• Shortest Delivery Tour — Hard
• Balanced Bracket Count — Hard
• Nim Game — Hard
• Treasure Grid — Hard
• Job Sequencing — Hard