Queues

Design a RecentCounter class to count the number of recent requests within a 3000ms sliding window. The class should have one method ping(t: number) that records a request at time t (t is strictly increasing across calls) and returns the number of requests in the inclusive range [t - 3000, t]. Use a queue (FIFO) to drop requests that have aged out — pop from the front in amortized O(1).

Given an integer n, return the least number of perfect square numbers (for example 1, 4, 9, 16) that sum to n. A perfect square is an integer that is the square of an integer.

Design a circular queue of fixed capacity k. Implement enQueue(value) (returns false if full), deQueue() (returns false if empty), Front() and Rear() (return -1 if empty), isEmpty(), and isFull().

Design a hit counter that counts hits received in the past 5 minutes (300 seconds). Implement hit(timestamp) to record a hit at the given time and getHits(timestamp) to return the number of hits in the previous 300 seconds (inclusive). Calls arrive in nondecreasing timestamp order.