백준 10845

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

using namespace std;

class Queue
{
private:
	int* queue;
	int first = 0, end = 0;
	int index = 0;
	int output = 0;

public:
	Queue(int num)
	{
		queue = new int[num];
	}
	~Queue()
	{
		delete[] queue;
	}

public:
	void Push(int num)
	{
		queue[index] = num;
		index++;
	}
	int Pop()
	{
		if (first == index)
		{
			return -1;
		}
		else
		{
			output = queue[first];
			first++;
			return output;
		}
	}
	int Size()
	{
		if ((index - first) <= 0)
		{
			return 0;
		}
		return (index - first);
	}
	bool empty()
	{
		if (Size() == 0)
		{
			return true;
		}
		else
		{
			return false;
		}
	}
	int front()
	{
		if (Size() == 0)
		{
			return -1;
		}
		return queue[first];
	}
	int back()
	{
		if (Size() == 0)
		{
			return -1;
		}
		return queue[index-1];
	}




};

int main(void)
{
	ios::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);

	int input = 0;

	cin >> input;

	Queue q(input);

	for (int i = 0; i < input; ++i)
	{
		string order;
		cin >> order;

		if (order == "push")
		{
			int num = 0;
			cin >> num;
			q.Push(num);
		}
		else if (order == "pop")
		{
			cout << q.Pop() << "\n";
		}
		else if (order == "size")
		{
			cout << q.Size() << "\n";
		}
		else if (order == "empty")
		{
			cout << q.empty() << "\n";
		}
		else if (order == "front")
		{
			cout << q.front() << "\n";
		}
		else if (order == "back")
		{
			cout << q.back() << "\n";
		}


	}
	
	

	return 0;
}