379.Leetcode

// Comments are added so that any beginner would understand the logic of the code.
#include <unordered_set> // The set is not in order but has unique elements.
#include <queue> // It works on FIFO principle.
#include <stdexcept>

class PhoneDirectory {
public:
    // Constructor for the PhoneDirectory class.
    // Initializes the phone directory with 'maxNumbers' available phone numbers.
    // Complexity: O(maxNumbers)
    PhoneDirectory(int maxNumbers) {
        m_maxNumbers = maxNumbers;

        // Initialize available numbers and the number queue.
        for (int i = 0; i < m_maxNumbers; ++i) {
            m_availableNumbers.insert(i);    // Mark 'i' as available.
            m_numberQueue.push(i);           // Add 'i' to the queue.
        }
    }

    // Get an available phone number. Returns -1 if no numbers are available.
    // Complexity: O(1)
    int get() {
        if (m_availableNumbers.empty()) {
            return INVALID_NUMBER;  // No available numbers.
        }
        int num = m_numberQueue.front();
        m_numberQueue.pop();
        m_availableNumbers.erase(num);  // Mark 'num' as used.
        return num;
    }

    // Check if a specific number is available.
    bool check(int number) {
        return m_availableNumbers.count(number) > 0;
    }

    // Release a previously assigned number, making it available again.
    // Throws exceptions for invalid input.
    void release(int number) {
        if (number < 0 || number >= m_maxNumbers) {
            throw std::out_of_range("Invalid number");  // Handle out-of-range numbers.
        }
        if (m_availableNumbers.count(number) == 0) {
            throw std::invalid_argument("Number is not in use");  // Handle invalid release.
        }
        m_availableNumbers.insert(number);  // Mark 'number' as available.
        m_numberQueue.push(number);         // Add 'number' to the queue.
    }

private:
    int m_maxNumbers;                    // Maximum allowed phone numbers.
    std::unordered_set<int> m_availableNumbers; // Set to track available numbers.
    std::queue<int> m_numberQueue;        // Queue to manage available numbers.
    const int INVALID_NUMBER = -1;        // Use a named constant instead of -1.
};