Easy data structure and algorithm practice puzzle.
Given a list of ping times in milliseconds, oldest first, and the current time, return how many pings landed in the last 3000 milliseconds, counting exactly 3000 ago. Push each ping onto a queue, and drop pings off the front while they're older than now - 3000. Whatever's left in the queue is your answer.
Solve it three ways: snap the jigsaw pieces together, fill in the blanks, or type it from scratch against the tests. This one is free.
Every line of the solution comes with a note explaining why it is there, and a step by step replay shows the code running. At level 3, where you type it yourself, you can ask for an AI mock interview on this problem that ends with a hiring manager's scorecard.
Then grow it into a real project with the Software Engineer button: this puzzle becomes the Ticket Integrity Check, a pipeline you can run and download. See every Software Engineer project.
Browse all 576 puzzles