Give an algorithm for reversing a queue Q. Only following standard operations are allowed on queue.
- enqueue(x) : Add an item x to rear of queue.
- dequeue() : Remove an item from front of queue.
- empty() : Checks if a queue is empty or not.
Examples:
Input : Q = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100] Output :Q = [100, 90, 80, 70, 60, 50, 40, 30, 20, 10] Input :[1, 2, 3, 4, 5] Output :[5, 4, 3, 2, 1]
C++
// CPP program to reverse a Queue #include <bits/stdc++.h> using namespace std; // Utility function to print the queue void Print(queue<int>& Queue) { while (!Queue.empty()) { cout << Queue.front() << " "; Queue.pop(); } } // Function to reverse the queue void reverseQueue(queue<int>& Queue) { stack<int> Stack; while (!Queue.empty()) { Stack.push(Queue.front()); Queue.pop(); } while (!Stack.empty()) { Queue.push(Stack.top()); Stack.pop(); } } // Driver code int main() { queue<int> Queue; Queue.push(10); Queue.push(20); Queue.push(30); Queue.push(40); Queue.push(50); Queue.push(60); Queue.push(70); Queue.push(80); Queue.push(90); Queue.push(100); reverseQueue(Queue); Print(Queue); } |
Java
// Java program to reverse a Queue import java.util.LinkedList; import java.util.Queue; import java.util.Stack; // Java program to reverse a queue public class Queue_reverse { static Queue<Integer> queue; // Utility function to print the queue static void Print() { while (!queue.isEmpty()) { System.out.print( queue.peek() + ", "); queue.remove(); } } // Function to reverse the queue static void reversequeue() { Stack<Integer> stack = new Stack<>(); while (!queue.isEmpty()) { stack.add(queue.peek()); queue.remove(); } while (!stack.isEmpty()) { queue.add(stack.peek()); stack.pop(); } } // 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); reversequeue(); Print(); } } //This code is contributed by Sumit Ghosh |
Python3
# Python3 program to reverse a queue
from queue import Queue
# Utility function to print the queue
def Print(queue):
while (not queue.empty()):
print(queue.queue[0], end = “, “)
queue.get()
# Function to reverse the queue
def reversequeue(queue):
Stack = []
while (not queue.empty()):
Stack.append(queue.queue[0])
queue.get()
while (len(Stack) != 0):
queue.put(Stack[-1])
Stack.pop()
# Driver code
if __name__ == ‘__main__’:
queue = Queue()
queue.put(10)
queue.put(20)
queue.put(30)
queue.put(40)
queue.put(50)
queue.put(60)
queue.put(70)
queue.put(80)
queue.put(90)
queue.put(100)
reversequeue(queue)
Print(queue)
# This code is contributed by PranchalK
C#
// c# program to reverse a Queue using System; using System.Collections.Generic; public class GFG { public static LinkedList<int> queue; // Utility function to print the queue public static void Print() { while (queue.Count > 0) { Console.Write(queue.First.Value + ", "); queue.RemoveFirst(); } } // Function to reverse the queue public static void reversequeue() { Stack<int> stack = new Stack<int>(); while (queue.Count > 0) { stack.Push(queue.First.Value); queue.RemoveFirst(); } while (stack.Count > 0) { queue.AddLast(stack.Peek()); stack.Pop(); } } // Driver code public static void Main(string[] args) { queue = new LinkedList<int>(); queue.AddLast(10); queue.AddLast(20); queue.AddLast(30); queue.AddLast(40); queue.AddLast(50); queue.AddLast(60); queue.AddLast(70); queue.AddLast(80); queue.AddLast(90); queue.AddLast(100); reversequeue(); Print(); } } // This code is contributed by Shrikant13 |
Output:
100, 90, 80, 70, 60, 50, 40, 30, 20, 10
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