백준 18258 c++

#include <iostream>
#include <vector> //erase는 시간이 많이 걸림
#include <deque>
#include <string>
//#include <queue>//queue 구현이 목표이므로 사용 불가

using namespace std;

int input(int lower, int upper);
void input_instructor(vector <string>& instructor, int size);
void print_instructor_result(vector <string> instructor);

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

	int N;
	vector <string> instructor;

	N = input(1, 2000000);
	input_instructor(instructor, N);
	print_instructor_result(instructor);

	return 0;
}

int input(int lower, int upper)
{
	//cout << "input" << endl;
	int A;

	while (1)
	{
		cin >> A;
		if (A >= lower && A <= upper)
		{
			break;
		}
		else
		{
			;
		}
	}

	return A;
}

void input_instructor(vector <string>& instructor, int size)
{
	//cout << "input_instructor" << endl;
	int i;
	string temp, integer;

	for (i = 0; i < size; i++)
	{
		cin >> temp;
		if (temp == "push")
		{
			instructor.push_back(temp);
			cin >> integer;
			instructor.push_back(integer);
		}
		else
		{
			instructor.push_back(temp);
		}
	}

	return;
}

void print_instructor_result(vector <string> instructor)
{
	//cout << "print_instructor_result" << endl;
	string temp;
	int i = 0, total_size = instructor.size();
	deque <int> psuedo_queue;

	while (i < total_size)
	{
		temp = instructor[i];
		if (temp == "push")//push
		{
			i++;
			psuedo_queue.push_back(stoi(instructor[i]));
		}
		else if(temp == "pop")//pop //출력
		{
			if (psuedo_queue.empty())
			{
				cout << "-1" << "\n";
			}
			else
			{
				cout << psuedo_queue.front() << "\n";
				psuedo_queue.pop_front(); //erase는 시간이 오래 걸림
			}
		}
		else if (temp == "size")//size //출력
		{
			cout << psuedo_queue.size() << "\n";
		}
		else if (temp == "empty")//empty //출력
		{
			if (psuedo_queue.empty())
			{
				cout << "1" << "\n";
			}
			else
			{
				cout << "0" << "\n";
			}
		}
		else if (temp == "front")//front //출력
		{
			if (psuedo_queue.empty())
			{
				cout << "-1" << "\n";
			}
			else
			{
				cout << psuedo_queue.front() << "\n";
			}
		}
		else//back //출력
		{
			if (psuedo_queue.empty())
			{
				cout << "-1" << "\n";
			}
			else
			{
				cout << psuedo_queue.back() << "\n";
			}
		}
		i++;
	}

	return;
}