使用递归反转队列

给定一个队列，编写一个递归函数将其反转。
允许标准操作：
enqueue(x)：将项目x添加到队列的后面。
dequeue()：从队列前面删除一个项目。
empty()：检查队列是否为空。

例子 ：

Input : Q = [5, 24, 9, 6, 8, 4, 1, 8, 3, 6]
Output : Q = [6, 3, 8, 1, 4, 8, 6, 9, 24, 5]

Explanation : Output queue is the reverse of the input queue.

Input : Q = [8, 7, 2, 5, 1]
Output : Q = [1, 5, 2, 7, 8]

递归算法：

1. 如果队列中有元素，则从队列中弹出元素，否则返回空队列。
2. 调用剩余队列的reverseQueue函数。
3. 将弹出的元素推入结果反转的队列中。

伪代码：

queue reverseFunction(queue)
{
    if (queue is empty)
       return queue;
    else {
       data = queue.front()
       queue.pop()
       queue = reverseFunction(queue);
       q.push(data);
       return queue;
    }
}

C++

// C++ code for reversing a queue
#include 
using namespace std;
  
// Utility function to print the queue
void printQueue(queue Queue)
{
    while (!Queue.empty()) {
        cout << Queue.front() << " ";
        Queue.pop();
    }
}
  
// Recursive function to reverse the queue
void reverseQueue(queue& q)
{
    // Base case
    if (q.empty())
        return;
  
    // Dequeue current item (from front)  
    long long int data = q.front();
    q.pop();
  
    // Reverse remaining queue  
    reverseQueue(q);
  
    // Enqueue current item (to rear)  
    q.push(data);
}
  
// Driver code
int main()
{
    queue Queue;
    Queue.push(56);
    Queue.push(27);
    Queue.push(30);
    Queue.push(45);
    Queue.push(85);
    Queue.push(92);
    Queue.push(58);
    Queue.push(80);
    Queue.push(90);
    Queue.push(100);
    reverseQueue(Queue);
    printQueue(Queue);
}

Java

// Java program to reverse a Queue by recursion
import java.util.LinkedList;
import java.util.Queue;
import java.util.Stack;
   
// Java program to reverse a queue recursively
public class Queue_reverse {
   
    static Queue queue;
   
    // Utility function to print the queue
    static void Print()
    {
        while (!queue.isEmpty()) 
        {
            System.out.print(queue.peek() + " ");
            queue.remove();
        }
    }
   
// Recurrsive function to reverse the queue
static Queue reverseQueue(Queue q)
{
    // Base case
    if (q.isEmpty())
        return q;
  
    // Dequeue current item (from front)  
    int data = q.peek();
    q.remove();
  
    // Reverse remaining queue  
    q = reverseQueue(q);
  
    // Enqueue current item (to rear)  
    q.add(data);
          
    return q;
}
   
// Driver code
public static void main(String args[])
{
    queue = new LinkedList();
    queue.add(56);
    queue.add(27);
    queue.add(30);
    queue.add(45);
    queue.add(85);
    queue.add(92);
    queue.add(58);
    queue.add(80);
    queue.add(90);
    queue.add(100);
    queue = reverseQueue(queue);
    Print();
}
}

Python3

# Queue Class
class Queue:
    def __init__(self):
        self.items = []
  
  
    def isEmpty(self):
        return self.items == []
  
    def add(self, item):
        self.items.append(item)
  
    def pop(self):
        return self.items.pop(0)
  
    def front(self):
        return self.items[0]
  
    def printQueue(self):
        for i in self.items:
            print(i, end =" ")
        print("")
  
  
# Recursive Function to reverse the queue
def reverseQueue(q):
  
    # Base case
    if (q.isEmpty()):
        return
  
    # Dequeue current item (from front) 
    data = q.front();
    q.pop();
  
    # Reverse remaining queue  
    reverseQueue(q)
  
    # Enqueue current item (to rear)  
    q.add(data)
  
  
# Driver Code
q = Queue()
q.add(56)
q.add(27)
q.add(30)
q.add(45)
q.add(85)
q.add(92)
q.add(58)
q.add(80)
q.add(90)
q.add(100)
reverseQueue(q)
q.printQueue()

C#

// C# code for reversing a queue
using System;
using System.Collections.Generic;
  
class GFG
{
    // Utility function 
    // to print the queue
    static void printQueue(Queue queue)
    {
        while (queue.Count != 0) 
        {
            Console.Write(queue.Peek() + " ");
            queue.Dequeue();
        }
    }
      
    // Recursive function 
    // to reverse the queue
    static void reverseQueue(ref Queue q)
    {
        // Base case
        if (q.Count == 0)
            return;
      
        // Dequeue current 
        // item (from front) 
        long data = q.Peek();
        q.Dequeue();
      
        // Reverse remaining queue 
        reverseQueue(ref q);
      
        // Enqueue current
        // item (to rear) 
        q.Enqueue(data);
    }     
      
    // Driver code
    static void Main()
    {
        Queue queue = new Queue();
        queue.Enqueue(56);
        queue.Enqueue(27);
        queue.Enqueue(30);
        queue.Enqueue(45);
        queue.Enqueue(85);
        queue.Enqueue(92);
        queue.Enqueue(58);
        queue.Enqueue(80);
        queue.Enqueue(90);
        queue.Enqueue(100);
        reverseQueue(ref queue);
        printQueue(queue);
    }
}
  
// This code is contributed by 
// Manish Shaw(manishshaw1)

输出：

100 90 80 58 92 85 45 30 27 56

时间复杂度： O(n)。
视频：