使用单队列实现堆栈

我们得到了队列数据结构，任务是仅使用给定的队列数据结构来实现堆栈。
我们已经讨论了使用两个队列的解决方案。在本文中，讨论了一种仅使用一个队列的新解决方案。这个解决方案假设我们可以在任何时候找到队列的大小。这个想法是将新插入的元素始终保持在队列的前面，保持先前元素的顺序相同。下面是完整的步骤。

// x is the element to be pushed and s is stack
push(s, x) 
  1) Let size of q be s. 
  1) Enqueue x to q
  2) One by one Dequeue s items from queue and enqueue them.
  
// Removes an item from stack
pop(s)
  1) Dequeue an item from q

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下面是这个想法的实现。

C++

// C++ program to implement a stack using
// single queue
#include
using namespace std;
 
// User defined stack that uses a queue
class Stack
{
    queueq;
public:
    void push(int val);
    void pop();
    int top();
    bool empty();
};
 
// Push operation
void Stack::push(int val)
{
    //  Get previous size of queue
    int s = q.size();
 
    // Push current element
    q.push(val);
 
    // Pop (or Dequeue) all previous
    // elements and put them after current
    // element
    for (int i=0; i


Java
// Java program to implement stack using a
// single queue
 
import java.util.LinkedList;
import java.util.Queue;
 
public class stack
{
    Queue q = new LinkedList();
     
    // Push operation
    void push(int val)
    {
        // get previous size of queue
        int size = q.size();
         
        // Add current element
        q.add(val);
         
        // Pop (or Dequeue) all previous
        // elements and put them after current
        // element
        for (int i = 0; i < size; i++)
        {
            // this will add front element into
            // rear of queue
            int x = q.remove();
            q.add(x);
        }
    }
     
    // Removes the top element
    int pop()
    {
        if (q.isEmpty())
        {
            System.out.println("No elements");
            return -1;
        }
        int x = q.remove();
        return x;
    }
     
    // Returns top of stack
    int top()
    {
        if (q.isEmpty())
            return -1;
        return q.peek();
    }
     
    // Returns true if Stack is empty else false
    boolean isEmpty()
    {
        return q.isEmpty();
    }
 
    // Driver program to test above methods
    public static void main(String[] args)
    {
        stack s = new stack();
        s.push(10);
        s.push(20);
        System.out.println("Top element :" + s.top());
        s.pop();
        s.push(30);
        s.pop();
        System.out.println("Top element :" + s.top());
    }
}
 
// This code is contributed by Rishabh Mahrsee

Python3
# Python3 program to implement stack using a
# single queue
  
q = []
 
# append operation
def append(val):
 
    # get previous size of queue
    size = len(q)
 
    # Add current element
    q.append(val);
 
    # Pop (or Dequeue) all previous
    # elements and put them after current
    # element
    for i in range(size):
 
        # this will add front element into
        # rear of queue
        x = q.pop(0);
        q.append(x);
            
# Removes the top element
def pop():
 
    if (len(q) == 0):
 
        print("No elements");
        return -1;
     
    x = q.pop(0);
    return x;
 
# Returns top of stack
def top():
 
    if(len(q) == 0):
        return -1;
    return q[-1]
 
# Returns true if Stack is empty else false
def isEmpty():
 
    return len(q)==0;
 
# Driver program to test above methods
if __name__=='__main__':
 
    s = []
 
    s.append(10);
    s.append(20);
    print("Top element :" + str(s[-1]));
    s.pop();
    s.append(30);
    s.pop();
    print("Top element :" + str(s[-1]));
     
    # This code is contributed by rutvik_56.

C#
// C# program to implement stack using a
// single queue
using System;
using System.Collections.Generic;
 
public class stack
{
    Queue q = new Queue();
     
    // Push operation
    void push(int val)
    {
        // get previous size of queue
        int size = q.Count;
         
        // Add current element
        q.Enqueue(val);
         
        // Pop (or Dequeue) all previous
        // elements and put them after current
        // element
        for (int i = 0; i < size; i++)
        {
            // this will add front element into
            // rear of queue
            int x = q.Dequeue();
            q.Enqueue(x);
        }
    }
     
    // Removes the top element
    int pop()
    {
        if (q.Count == 0)
        {
            Console.WriteLine("No elements");
            return -1;
        }
        int x = q.Dequeue();
        return x;
    }
     
    // Returns top of stack
    int top()
    {
        if (q.Count == 0)
            return -1;
        return q.Peek();
    }
     
    // Returns true if Stack is empty else false
    bool isEmpty()
    {
        if(q.Count == 0)
            return true;
        return false;
    }
 
    // Driver program to test above methods
    public static void Main(String[] args)
    {
        stack s = new stack();
        s.push(10);
        s.push(20);
        Console.WriteLine("Top element :" + s.top());
        s.pop();
        s.push(30);
        s.pop();
        Console.WriteLine("Top element :" + s.top());
    }
}
 
// This code has been contributed by Rajput-Ji

Javascript

输出：

20
10