Coding Katas
12 algorithm challenges — ported from Node.js + Jest to an interactive in-browser playground. Inputs are editable; click any preset to load an example.
Basketball Points
Given 2-pointers and 3-pointers scored, return the total score.
Hitting the Jackpot
Returns true if all 4 slot-machine elements are identical.
Game of Thrones Titles
Capitalise words except "and", "the", "of", "in". Commas followed by a space. Ends with period.
Second Largest
Returns the second largest number from an array (handles duplicates).
Rearrange the Sentence
Each word has an embedded digit indicating its position. Return them in order.
Count Instances
Count how many times a single character appears in a string.
Give Me a Hint
Returns an array of strings that progressively reveal each word one letter at a time.
IPv4 Validation
Returns true if a string is a valid IPv4 address (4 octets, 0–255, no leading zeros, last octet not 0).
Anagram Finder
Find all words in the list that are anagrams of the input word.
Unlucky Years
Returns the number of Friday the 13ths in a given year.
X and Os
Click cells to cycle X → O → empty. Find the winning move for X (2 X's already in a winning line, no blocking O).
Click to cycle: empty → X → O → empty
Capital Front, Numbers Back
Reorder a string: uppercase letters first, lowercase in the middle, digits at the end.