Queue· 15 min

Number of Recent Calls

LeetCode #933 · Easy · Interactive step-by-step visualization

Setup

Example inputping(1), ping(100), ping(3001), ping(3002)
Step 1 / 16

Current step

1 / 16

Hold requests in a queue. Pings arrive in increasing time order, so the oldest request is always at the front. Only requests inside the 3000 ms window need to be counted.

Step log

ping(t) calls

1
0
100
1
3001
2
3002
3

requests within the last 3000 ms

front · exitemptyrear · enter

window

[t - 3000, t]

Named pointer
Active node
Committed or completed
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number-of-recent-calls.java
1class RecentCounter {
2    private final Deque<Integer> requests = new ArrayDeque<>();
3 
4    public int ping(int t) {
5        requests.addLast(t);
6        while (requests.peekFirst() < t - 3000)
7            requests.pollFirst();
8        return requests.size();
9    }
10}
● Java
Time
O(1) amortized
Space
O(n)
Pattern
queue
Frames
16
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