C/C++ 큐

코드

#include <bits/stdc++.h>
#define ll long long
using namespace std;
#define X first
#define Y second
class node
{
public:
    int data;
    node* link;
    node(int data = 0) : link(nullptr), data(data) {}
};

class que
{
public:
    node* f;
    node* b;
    que()
    {
        f = new node();
        b = f;
    }
    void push(int data)
    {
        node* new_node = new node(data);
        if (f->link == nullptr)
        {
            f->link = new_node;
            b = new_node;
            return;
        }
        b->link = new_node;
        b = new_node;
       
    }
    void pop()
    {
        if (f->link == nullptr)
        {
            cout << -1 << "\n";
            return;
        }
        node* df = f->link;
        cout << df->data << "\n";
        f->link = f->link->link;
        delete df;
    }
    void size()
    {
        node* tmp = f;
        int size = 0;
        while (tmp->link != nullptr)
        {
            size++;
            tmp = tmp->link;
        }
        cout << size << "\n";
    }
    void empty()
    {
        if (f->link == nullptr)
            cout << "1\n";
        else
            cout << "0\n";
    }
    void front()
    {
        if (f->link == nullptr)
        {
            cout << "-1\n";
            return;
        }
           
        cout << f->link->data << "\n";
    }
    void back()
    {
        if (f->link == nullptr)
        {
            cout << "-1\n";
            return;
        }
        cout << b->data << "\n";
    }
};
int main(void) {
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    int n; cin >> n;
    que q;
    for (int i = 0; i < n; i++)
    {
        string s; cin >> s;
        if (s == "push")
        {
            int x; cin >> x;
            q.push(x);
        }
        else if (s == "pop")
        {
            q.pop();
        }
        else if (s == "size")
        {
            q.size();
        }
        else if (s == "empty")
        {
            q.empty();
        }
        else if (s == "front")
            q.front();
        else if (s == "back")
        {
            q.back();
        }
    }
    return 0;
}

사이즈 함수는 O(1)로도 구현이 가능하나 테스트를 위해 O(N)으로 구현했습니다.

연습문제 boj 카드 2

#include <bits/stdc++.h>
#define ll long long
using namespace std;
#define X first
#define Y second
class node
{
public:
    int data;
    node* link;
    node(int data = 0) : link(nullptr), data(data) {}
};

class que
{
public:
    node* f;
    node* b;
    int q_size;
    que() : q_size(0)
    {
        f = new node();
        b = f;
    }

    void push(int data)
    {
        node* new_node = new node(data);
        if (f->link == nullptr)
        {
            f->link = new_node;
            b = new_node;
        }
        else
        {
            b->link = new_node;
            b = new_node;
        }
        q_size++;
    }

    void pop()
    {
        if (f->link == nullptr)
        {
            cout << -1 << "\n";
            return;
        }
        node* df = f->link;
        f->link = f->link->link;
        delete df;
        q_size--;
    }

    void size()
    {
        cout << q_size << "\n";
    }

    void empty()
    {
        if (f->link == nullptr)
            cout << "1\n";
        else
            cout << "0\n";
    }

    void front()
    {
        if (f->link == nullptr)
        {
            cout << "-1\n";
            return;
        }

        cout << f->link->data << "\n";
    }

    void back()
    {
        if (f->link == nullptr)
        {
            cout << "-1\n";
            return;
        }
        cout << b->data << "\n";
    }
    void solve()
    {
        while (q_size > 1)
        {
            pop();
            push(f->link->data);
            pop();
        }
        cout << f->link->data;
    }
};
int main(void) {
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    int n; cin >> n;
    que q;
    for (int i = 1; i <= n; i++)
        q.push(i);
    q.solve();
    return 0;
}