Number of Recent Calls

Problem Summary

(Write in your own words, not copied from LeetCode. This forces comprehension.)

• You're to build an object that lets you ping at a certain time. You have to return how many pings you got in the last 3000ms.

Why This Works

(Explain the core reason the solution is correct.)

• You are guaranteed to get increasing ping time.
• Therefore, you don't need to store anything less than 3000 of every ping received

Main Concepts Used

(Mark the CS concepts or algorithms used.)

• Queue

Time & Space Complexity

• Time: $O(1)$ → Reason:
• Space: $O(1)$ → Reason:

Code

class RecentCounter:
    rangeInMs = 3000

    def __init__(self):
        self.queue = deque()

    def ping(self, t: int) -> int:
        self.queue.append(t)
        rangeStart = t - self.rangeInMs

        while self.queue and self.queue[0] < rangeStart:
            self.queue.popleft()

        return len(self.queue)

Common Mistakes / Things I Got Stuck On