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# Append the elements of queue in mirror-inverse order

• Difficulty Level : Easy
• Last Updated : 13 Aug, 2021

Given a queue Q containing N strings, the task is to restructure the queue to double its size such that the second half represents the mirror image of the first half.
Examples:

Input: Q = {“Hello”, “World”}
Output: {“Hello”, “World”, “World”, “Hello”}
Explanation:
The second half of the output queue is the mirror image of the first half. That is:
“Hello”, “World” | “World”, “Hello”
Input: Q = {“Hi”, “Geeks”}
Output: {“Hi”, “Geeks”, “Geeks”, “Hi”}

Approach: On observing carefully, we can say that the second half of the output queue is the reverse of the first half. That is:

1. Store the size of the queue in a variable named size.
2. Push the Queue elements into a stack without actually losing the elements. This can be achieved by using emplace().
3. Repeat the process until size becomes 0.
4. Push the elements of the stack back to the queue.

Below is the implementation of the above approach.

## C++

 // C++ program to arrange the// elements of the queue// to the end such that// the halves are mirror// order of each other#include using namespace std; // Function to display// the elements of// the queuevoid showq(queue q){    // Iterating through the queue    // and printing the elements    while (!q.empty()) {        cout << q.front() << " ";        q.pop();    }} // Function to produce mirror elementsvoid mirrorQueue(queue& q){    int size = q.size();     // Defining a stack    stack st;     // Pushing the elements    // of a queue    // in a stack without    // losing them    // from the queue    while (size--) {        string x = q.front();        // Push the element        // to the end of the        // queue        q.emplace(x);        // Push the element        // into the stack        st.push(x);        // Remove the element        q.pop();    }     // Appending the elements    // from the stack    // to the queue    while (!st.empty()) {        string el = st.top();        q.push(el);        st.pop();    }} // Driver Codeint main(){    queue q;    q.push("Hello");    q.push("World");    mirrorQueue(q);    showq(q);    return 0;}

## Java

 // Java program to arrange the// elements of the queue// to the end such that// the halves are mirror// order of each otherimport java.util.*;class GFG{ // Function to display// the elements of// the queuestatic void showq(Queue q){    // Iterating through the queue    // and printing the elements    while (!q.isEmpty())    {        System.out.print(q.peek() + " ");        q.remove();    }} // Function to produce mirror elementsstatic void mirrorQueue(Queue q){    int size = q.size();     // Defining a stack    Stack st = new Stack<>();     // Pushing the elements    // of a queue    // in a stack without    // losing them    // from the queue    while (size-->0)    {        String x = q.peek();               // Push the element        // to the end of the        // queue        q.add(x);               // Push the element        // into the stack        st.add(x);               // Remove the element        q.remove();    }     // Appending the elements    // from the stack    // to the queue    while (!st.isEmpty())    {        String el = st.peek();        q.add(el);        st.pop();    }} // Driver Codepublic static void main(String[] args){    Queue q =          new inkedList();    q.add("Hello");    q.add("World");    mirrorQueue(q);    showq(q);}} // This code is contributed by gauravrajput1

## Python3

 # Python3 program to arrange the# elements of the queue# to the end such that# the halves are mirror# order of each other # Function to display# the elements of# the queuedef showq(q) :     # Iterating through the queue    # and printing the elements    while (len(q) != 0) :             print(q[0] , end = " ")        q.pop(0)         # Function to produce mirror elementsdef mirrorQueue(q) :     size = len(q)      # Defining a stack    st = []      # Pushing the elements    # of a queue    # in a stack without    # losing them    # from the queue    while (size > 0) :             x = q[0]                # Push the element        # to the end of the        # queue        q.append(x)                # Push the element        # into the stack        st.append(x)                # Remove the element        q.pop(0)                 size -= 1      # Appending the elements    # from the stack    # to the queue    while (len(st) != 0) :             el = st[len(st) - 1]        q.append(el)        st.pop()         q = []q.append("Hello")q.append("World")mirrorQueue(q)showq(q) # This code is contributed by divyeshrabadiya07

## C#

 // C# program to arrange the// elements of the queue// to the end such that// the halves are mirror// order of each otherusing System;using System.Collections.Generic;class GFG{ // Function to display// the elements of// the queuestatic void showq(Queue q){  // Iterating through the queue  // and printing the elements  while (q.Count != 0)  {    Console.Write(q.Peek() + " ");    q.Dequeue();  }} // Function to produce mirror elementsstatic void mirrorQueue(Queue q){  int size = q.Count;   // Defining a stack  Stack st = new Stack();   // Pushing the elements  // of a queue  // in a stack without  // losing them  // from the queue  while (size --> 0)  {    String x = q.Peek();     // Push the element    // to the end of the    // queue    q.Enqueue(x);     // Push the element    // into the stack    st.Push(x);     // Remove the element    q.Dequeue();  }   // Appending the elements  // from the stack  // to the queue  while (st.Count != 0)  {    String el = st.Peek();    q.Enqueue(el);    st.Pop();  }} // Driver Codepublic static void Main(String[] args){  Queue q = new Queue();  q.Enqueue("Hello");  q.Enqueue("World");  mirrorQueue(q);  showq(q);}} // This code is contributed by Rajput-Ji

## Javascript


Output:
Hello World World Hello

Time Complexity: O(N), where N is the size of the queue
Auxiliary Space: O(N)

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