LeetCode 2694: Event Emitter Solution

Master LeetCode problem 2694 (Event Emitter), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

2694. Event Emitter

Medium

Problem Explanation

Explanation

To implement the EventEmitter class, we can use a HashMap where the keys are event names and the values are lists of callback functions. When subscribing to an event, we add the callback function to the list of callbacks for that event. When emitting an event, we iterate through the list of callbacks for that event and call each callback with the provided arguments. Unsubscribing removes a specific callback function from the list of callbacks for the event.

Time Complexity

Subscribing: O(1)
Emitting: O(n) where n is the number of callbacks for the event
Unsubscribing: O(n) where n is the number of callbacks for the event

Space Complexity

O(m * n) where m is the number of events and n is the number of callbacks for each event

Solution Code

import java.util.*;

class EventEmitter {
    Map<String, List<Callback>> eventCallbacks;

    public EventEmitter() {
        eventCallbacks = new HashMap<>();
    }

    public void subscribe(String eventName, Callback callback) {
        eventCallbacks.putIfAbsent(eventName, new ArrayList<>());
        eventCallbacks.get(eventName).add(callback);
    }

    public void emit(String eventName, Object... args) {
        List<Object> results = new ArrayList<>();
        List<Callback> callbacks = eventCallbacks.getOrDefault(eventName, new ArrayList<>());
        for (Callback cb : callbacks) {
            results.add(cb.call(args));
        }
        System.out.println(results); // Returning results for demonstration
    }

    public void unsubscribe(String eventName, int index) {
        if (eventCallbacks.containsKey(eventName)) {
            List<Callback> callbacks = eventCallbacks.get(eventName);
            if (index >= 0 && index < callbacks.size()) {
                callbacks.remove(index);
            }
        }
    }

    private interface Callback {
        Object call(Object... args);
    }
}

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