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队列

视频讲解

🎥 视频讲解

队列

队列是一种先进先出（FIFO）的数据结构。

模板题

自建OJ：模拟队列

代码实现

手写实现 
#include <bits/stdc++.h>
using namespace std;

const int N = 1e5 + 10;
int q[N];
int hh, tt;
int n;

int main() {
    cin >> n;
    while (n--) {
        string s;
        cin >> s;
        if (s == "push") {
            int x;
            cin >> x;
            q[tt++] = x;
        } else if (s == "pop") {
            if (hh != tt) {
                hh++;
            }
        } else if (s == "empty") {
            if (hh == tt) {
                cout << "YES\n";
            } else {
                cout << "NO\n";
            }
        } else { // query
            if (hh == tt) {
                cout << "empty\n";
            } else {
                cout << q[hh] << "\n";
            }
        }
    }
    return 0;
}

import java.util.Scanner;

public class Main {

    static final int N = 100000 + 10;
    static int[] q = new int[N];
    static int hh = 0, tt = 0;

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();

        while (n-- > 0) {
            String s = sc.next();
            if (s.equals("push")) {
                int x = sc.nextInt();
                q[tt++] = x;
            } else if (s.equals("pop")) {
                if (hh != tt) {
                    hh++;
                }
            } else if (s.equals("empty")) {
                if (hh == tt) {
                    System.out.println("YES");
                } else {
                    System.out.println("NO");
                }
            } else { // query
                if (hh == tt) {
                    System.out.println("empty");
                } else {
                    System.out.println(q[hh]);
                }
            }
        }
    }
}

N = 100000 + 10
q = [0] * N
hh = 0
tt = 0

n = int(input())
for _ in range(n):
    s = input().split()
    if s[0] == "push":
        q[tt] = int(s[1])
        tt += 1
    elif s[0] == "pop":
        if hh != tt:
            hh += 1
    elif s[0] == "empty":
        if hh == tt:
            print("YES")
        else:
            print("NO")
    else:  # query
        if hh == tt:
            print("empty")
        else:
            print(q[hh])
模板库实现 
#include <bits/stdc++.h>
using namespace std;

queue<int> q;

int main()
{
    int m;
    cin >> m;

    while (m--)
    {
        string s;
        cin >> s;

        int x;

        if (s == "empty")
        {
            if (q.empty())
            {
                cout << "YES\n";
            }
            else
            {
                cout << "NO\n";
            }
        }
        else if (s == "push")
        {
            cin >> x;
            q.push(x);
        }
        else if (s == "query")
        {
            if (q.empty())
            {
                cout << "empty\n";
            }
            else
            {
                cout << q.front() << "\n";
            }
        }
        else if (s == "pop")
        {
            if (!q.empty())
            {
                q.pop();
            }
        }
    }

    return 0;
}

import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        Queue<Integer> q = new LinkedList<>();

        int m = sc.nextInt();
        while (m-- > 0) {
            String s = sc.next();
            if (s.equals("empty")) {
                if (q.isEmpty()) System.out.println("YES");
                else System.out.println("NO");
            } else if (s.equals("push")) {
                int x = sc.nextInt();
                q.offer(x);
            } else if (s.equals("query")) {
                if (q.isEmpty()) System.out.println("empty");
                else System.out.println(q.peek());
            } else if (s.equals("pop")) {
                if (!q.isEmpty()) q.poll();
            }
        }
    }
}

from collections import deque

q = deque()

m = int(input())
for _ in range(m):
    s = input().split()
    if s[0] == "empty":
        print("YES" if not q else "NO")
    elif s[0] == "push":
        q.append(int(s[1]))
    elif s[0] == "query":
        if not q:
            print("empty")
        else:
            print(q[0])
    elif s[0] == "pop":
        if q:
            q.popleft()

练习题单

队列