Reverse First K elements of Queue Java

PROGRAM TO REVERSE THE FIRST K ELEMENTS OF A QUEUE

import java.util.LinkedList;

import java.util.Queue;

import java.util.Stack;

 

public class Reverse_k_element_queue {

 

    static Queue<Integer> queue;

 

    // Function to reverse the first

    // K elements of the Queue

    static void reverseQueueFirstKElements(int k)

    {

        if (queue.isEmpty() == true

            || k > queue.size())

            return;

        if (k <= 0)

            return;

 

        Stack<Integer> stack = new Stack<Integer>();

 

        // Push the first K elements into a Stack

        for (int i = 0; i < k; i++) {

            stack.push(queue.peek());

            queue.remove();

        }

 

        // Enqueue the contents of stack

        // at the back of the queue

        while (!stack.empty()) {

            queue.add(stack.peek());

            stack.pop();

        }

 

        // Remove the remaining elements and enqueue

        // them at the end of the Queue

        for (int i = 0; i < queue.size() - k; i++) {

            queue.add(queue.peek());

            queue.remove();

        }

    }

 

    // Utility Function to print the Queue

    static void Print()

    {

        while (!queue.isEmpty()) {

            System.out.print(queue.peek() + " ");

            queue.remove();

        }

    }

 

    // Driver code

    public static void main(String args[])

    {

        queue = new LinkedList<Integer>();

        queue.add(10);

        queue.add(20);

        queue.add(30);

        queue.add(40);

        queue.add(50);

        queue.add(60);

        queue.add(70);

        queue.add(80);

        queue.add(90);

        queue.add(100);

 

        int k = 5;

        reverseQueueFirstKElements(k);

        Print();

    }

}




OUTPUT:

50 40 30 20 10 60 70 80 90 100

CREDITS: https://www.geeksforgeeks.org/reversing-first-k-elements-queue/