Implement the Observer Pattern

Hard Design Patterns & Final Challenges

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Problem Statement

Create an `Observer` interface with `virtual void update(std::string state) = 0`. Create `Subject` that holds a `std::vector` and has `attach(Observer*)` and `setState(std::string)`. When state changes, call `update()` on all observers. Instantiate `Subject` and two observers, set state based on input, and print notifications.

Input Format

A single string representing the state.

Output Format

Print notifications for 'Obs 1' and 'Obs 2' on separate lines.

Constraints

None

Sample Input

Ready

Sample Output

Obs 1: Ready
Obs 2: Ready

Explanation

The Observer pattern provides a subscription mechanism, coupling one subject to many observers loosely.

Starter Code

#include <iostream>
#include <vector>
#include <string>

class Observer {
public:
    virtual void update(std::string state) = 0;
};

// Implement ConcreteObserver and Subject

int main() {
    // Setup pattern and trigger state change
    return 0;
}

Limits

Time Limit: 1s
Memory Limit: 256MB

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