题解 | #【模板】队列#

很显然题目是想我们实现一个队列，那么直接调用STL库就十分的没有味道了。

我的方案是用一个链表来模拟队列，链表含队首指针和队尾指针（仅有队首指针会超时！），push是在队尾添加节点的操作，pop是在队首删除节点的操作，front是输出队首节点的操作。

#include <iostream>
#include <string>
using namespace std;
class node {
  public:
    int x;
    node* pnext = nullptr;
    node(int x) {
        this->x = x;
    }
};
class queue {
  private:
    node* pfront = nullptr; // 队首指针
    node* prear = nullptr; // 队尾指针
  public:
    void push(int x) {
        node* tmp = new node(x);
        if (pfront == nullptr) {
            pfront = tmp;
            prear = tmp;
        } else {
            prear->pnext = tmp;
            prear = tmp;
        }
    }
    void pop() {
        if (pfront == nullptr)
            cout << "error" << endl;
        else {
            cout << pfront->x << endl;
            if (pfront == prear) {
                free(pfront);
                pfront = nullptr;
                prear = nullptr;
            } else {
                node* tmp = pfront;
                pfront = pfront->pnext;
                free(tmp);
            }
        }
    }
    void front() {
        if (pfront == nullptr)
            cout << "error" << endl;
        else
            cout << pfront->x << endl;
    }
};

int main() {
    int n;
    cin >> n;
    queue q;
    for (int i = 0; i < n; i++) {
        string op;
        cin >> op;
        if (op == "push") {
            int x;
            cin >> x;
            q.push(x);
        } else if (op == "pop") {
            q.pop();
        } else if (op == "front") {
            q.front();
        }
    }
    return 0;
}