Free coding challenges.
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🗓️ This week's challenges
New picks every Monday · resets in --Sum a list
Add up every number in [4, 8, 15, 16, 23, 42].
Factorial
Compute 5! (5 factorial) with a loop or recursion.
Anagram Checker
Do two words use exactly the same letters, just rearranged?
Palindrome checker
Check whether each word reads the same backwards.
Merge Two Sorted Arrays
Combine two already-sorted arrays into one sorted array.
Binary Search
Find a value in a sorted array in O(log n) instead of scanning it.
Matrix Rotation
Rotate a 3x3 grid of numbers 90 degrees clockwise, in place.
Sieve of Eratosthenes
Find every prime number up to 50 -- efficiently, not by checking each one individually.
All challenges
FizzBuzz
The classic. Print numbers 1-15, but with a twist on multiples of 3 and 5.
Reverse a string
Print "hello world" backwards.
Sum a list
Add up every number in [4, 8, 15, 16, 23, 42].
Palindrome checker
Check whether each word reads the same backwards.
Count the vowels
How many a, e, i, o, u's are in a sentence?
Find the largest number
Find the biggest value in a list without a built-in max function.
Factorial
Compute 5! (5 factorial) with a loop or recursion.
Two Sum
A classic interview question: find two numbers that add up to a target.
Anagram Checker
Do two words use exactly the same letters, just rearranged?
Caesar Cipher
Shift every letter of a word forward by 3 in the alphabet.
Binary Search
Find a value in a sorted array in O(log n) instead of scanning it.
Balanced Parentheses
Classic stack problem: does every open paren have a matching close?
Merge Two Sorted Arrays
Combine two already-sorted arrays into one sorted array.
Longest Increasing Run
Find the longest stretch of strictly increasing numbers in a row.
Sieve of Eratosthenes
Find every prime number up to 50 -- efficiently, not by checking each one individually.
Longest Common Subsequence
Classic dynamic programming: the longest sequence of letters both strings share, in order.
Matrix Rotation
Rotate a 3x3 grid of numbers 90 degrees clockwise, in place.
Most Frequent Word
Find which word appears the most in a sentence -- and how many times.
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