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How to Solve Event Emitter Problem
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Medium#2694
LeetCode ProblemEvent Emitter
Design an EventEmitter class. This interface is similar (but with some differences) to the one found in Node.js or the Event Target interface of the DOM. The EventEmitter should allow for subscribing to events and emitting them. Your EventEmitter class should have the following two methods:
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Problem Breakdown
Understanding the Event Emitter Problem
Let's break down this LeetCode problem and understand what makes it challenging in interview settings.
Problem Statement
Design an EventEmitter class. This interface is similar (but with some differences) to the one found in Node.js or the Event Target interface of the DOM. The EventEmitter should allow for subscribing to events and emitting them. Your EventEmitter class should have the following two methods:
MediumProblem #2694
LeetCodeEvent Emitter
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Examples
# Example 1
Input
actions = ["EventEmitter", "emit", "subscribe", "subscribe", "emit"], values = [[], ["firstEvent"], ["firstEvent", "function cb1() { return 5; }"], ["firstEvent", "function cb1() { return 6; }"], ["firstEvent"]]Output
[[],["emitted",[]],["subscribed"],["subscribed"],["emitted",[5,6]]]
# Example 2
Input
actions = ["EventEmitter", "subscribe", "emit", "emit"], values = [[], ["firstEvent", "function cb1(...args) { return args.join(','); }"], ["firstEvent", [1,2,3]], ["firstEvent", [3,4,6]]]Output
[[],["subscribed"],["emitted",["1,2,3"]],["emitted",["3,4,6"]]]
# Example 3
Input
actions = ["EventEmitter", "subscribe", "emit", "unsubscribe", "emit"], values = [[], ["firstEvent", "(...args) => args.join(',')"], ["firstEvent", [1,2,3]], [0], ["firstEvent", [4,5,6]]]Output
[[],["subscribed"],["emitted",["1,2,3"]],["unsubscribed",0],["emitted",[]]]
# Example 4
Input
actions = ["EventEmitter", "subscribe", "subscribe", "unsubscribe", "emit"], values = [[], ["firstEvent", "x => x + 1"], ["firstEvent", "x => x + 2"], [0], ["firstEvent", [5]]]
Output
[[],["subscribed"],["subscribed"],["unsubscribed",0],["emitted",[7]]]
Constraints
1 <= actions.length <= 10
values.length === actions.length
All test cases are valid, e.g. you don't need to handle scenarios when unsubscribing from a non-existing subscription.
There are only 4 different actions: EventEmitter, emit, subscribe, and unsubscribe.
The EventEmitter action doesn't take any arguments.
The emit action takes between either 1 or 2 arguments. The first argument is the name of the event we want to emit, and the 2nd argument is passed to the callback functions.
The subscribe action takes 2 arguments, where the first one is the event name and the second is the callback function.
The unsubscribe action takes one argument, which is the 0-indexed order of the subscription made before.
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Frequently Asked Questions
Common questions about solving Event Emitter and using PhantomCodeAI during coding interviews.
How does PhantomCodeAI help me solve coding problems like Event Emitter during interviews?
PhantomCodeAI generates complete solutions instantly with proper complexity analysis, letting you focus on explaining your approach and demonstrating problem-solving skills rather than getting stuck on implementation details during high-pressure situations.
What if the interviewer asks follow-up questions or modifications to problems like Event Emitter?
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Can PhantomCodeAI help me communicate my solution for problems like Event Emitter?
Yes. PhantomCodeAI provides step-by-step approach explanations with 3 progressive thoughts, so you can walk through your solution naturally. It also provides time and space complexity analysis to discuss trade-offs.
How does PhantomCodeAI assist with different programming languages for Event Emitter type problems?
PhantomCodeAI supports 11 programming languages including Python, Java, C++, JavaScript, TypeScript, Go, Rust, Ruby, Swift, Kotlin, and C#. Set your preferred language and get idiomatic solutions.
What coding mistakes does PhantomCodeAI help me avoid during Event Emitter interviews?
PhantomCodeAI catches common mistakes like off-by-one errors, missing edge cases, incorrect base conditions, and suboptimal approaches. It provides clean, well-structured code that handles all edge cases.
Is PhantomCodeAI detectable when solving problems like Event Emitter during live interviews?
No. PhantomCodeAI runs as an invisible desktop overlay that doesn't appear in screen shares, recordings, or proctoring software. It works with Zoom, HackerRank, CodeSignal, CoderPad, and all major platforms.
How does PhantomCodeAI help when I'm struggling with Event Emitter style questions under pressure?
The AI provides structured guidance: first the approach (what algorithm/data structure to use and why), then the implementation with clean code, and finally complexity analysis. This helps you think clearly even under pressure.
Does PhantomCodeAI work for the coding platforms used in Event Emitter interviews?
Yes. PhantomCodeAI works with all major coding platforms including LeetCode, HackerRank, CodeSignal, CoderPad, HackerEarth, and any browser-based coding environment.
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