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Check if Queue Elements are pairwise consecutive
  • Last Updated : 19 Oct, 2020

Given a Queue of integers. The task is to check if consecutive elements in the queue are pairwise consecutive.
Examples: 

Input : 1 2 5 6 9 10
Output : Yes

Input : 2 3 9 11 8 7
Output : No

Approach: Using two stacks : 

  • Transfer all elements of the queue to one auxiliary stack aux.
  • Now, transfer the elements from this stack to another auxiliary stack aux2.
  • Start popping two elements from aux2 and then check the difference between these two elements. If their difference is 1, continue for other pairs till one element is left in the stack.
  • Also, after popping, push them to queue simultaneously to maintain the original queue.
  • Finally, if there is any pair with a difference not equal to 1, return false, else return true.

Below is the implementation of the above approach: 
 

C++




// C++ program to check if successive
// pair of numbers in the queue are
// consecutive or not
#include <bits/stdc++.h>
using namespace std;
 
// Function to check if elements are
// pairwise consecutive in queue
bool pairWiseConsecutive(queue<int> q)
{
    // Transfer elements of q to aux.
    stack<int> aux;
    while (!q.empty()) {
        aux.push(q.front());
        q.pop();
    }
 
    // Again transfer the
    // elements of aux to aux2
    stack<int> aux2;
    while (!aux.empty()) {
        aux2.push(aux.top());
        aux.pop();
    }
 
    // Traverse aux2 and see if
    // elements are pairwise
    // consecutive or not. We also
    // need to make sure that original
    // content is retained.
    bool result = true;
    while (aux2.size() > 1) {
 
        // Fetch current top two
        // elements of aux2 and check
        // if they are consecutive.
        int x = aux2.top();
        aux2.pop();
 
        int y = aux2.top();
        aux2.pop();
 
        if (abs(x - y) != 1)
            result = false;
 
        // Push the elements to queue
        q.push(x);
        q.push(y);
    }
 
    if (aux2.size() == 1)
        q.push(aux2.top());
 
    return result;
}
 
// Driver program
int main()
{
    // Pushing elements into the queue
    queue<int> q;
    q.push(4);
    q.push(5);
    q.push(-2);
    q.push(-3);
    q.push(11);
    q.push(10);
    q.push(5);
    q.push(6);
 
    if (pairWiseConsecutive(q))
        cout << "Yes" << endl;
    else
        cout << "No" << endl;
 
    // Printing the original queue
    while (!q.empty()) {
        cout << q.front() << " ";
        q.pop();
    }
    cout << endl;
 
    return 0;
}

Java




// Java program to check if successive
// pair of numbers in the queue are
// consecutive or not
 
import java.util.LinkedList;
import java.util.Queue;
import java.util.Stack;
 
 
public class GFG {
 
// Function to check if elements are
// pairwise consecutive in queue
static boolean pairWiseConsecutive(Queue<Integer> q)
{
    // Transfer elements of q to aux.
    Stack<Integer> aux = new Stack<>();
    while (!q.isEmpty()) {
        aux.push(q.peek());
        q.poll();
    }
 
    // Again transfer the
    // elements of aux to aux2
    Stack<Integer> aux2 = new Stack<>();
    while (!aux.empty()) {
        aux2.push(aux.peek());
        aux.pop();
    }
 
    // Traverse aux2 and see if
    // elements are pairwise
    // consecutive or not. We also
    // need to make sure that original
    // content is retained.
    boolean result = true;
    while (aux2.size() > 1) {
 
        // Fetch current top two
        // elements of aux2 and check
        // if they are consecutive.
        int x = aux2.peek();
        aux2.pop();
 
        int y = aux2.peek();
        aux2.pop();
 
        if (Math.abs(x - y) != 1)
            result = false;
 
        // Push the elements to queue
        q.add(x);
        q.add(y);
    }
 
    if (aux2.size() == 1)
        q.add(aux2.peek());
 
    return result;
}
 
// Driver program
  static public void main(String[] args) {
           // Pushing elements into the queue
    Queue<Integer> q= new LinkedList<Integer>();
    q.add(4);
    q.add(5);
    q.add(-2);
    q.add(-3);
    q.add(11);
    q.add(10);
    q.add(5);
    q.add(6);
 
    if (pairWiseConsecutive(q))
        System.out.println("Yes");
    else
        System.out.println("No");
 
    // Printing the original queue
    while (!q.isEmpty()) {
        System.out.print(q.peek() + " ");
        q.remove();
    }
    System.out.println();
 
    }
}
// This code is contributed by Rajput-Ji

Python3




# Python3 program to check
# if successive pair of numbers
# in the queue are consecutive or not
import queue
 
# Function to check if elements are
# pairwise consecutive in queue
def pairWiseConsecutive(q):
 
    # Transfer elements of
    # q to aux.
    aux = []
     
    while (q.qsize() != 0):
        aux.append(q.queue[0])
        q.get()
   
    # Again transfer the
    # elements of aux to aux2
    aux2 = []
     
    while (len(aux) != 0):
        aux2.append(aux[len(aux) - 1])
        aux.pop()
   
    # Traverse aux2 and see if
    # elements are pairwise
    # consecutive or not. We also
    # need to make sure that original
    # content is retained.
    result = bool(True)
    while (len(aux2) > 1):
   
        # Fetch current top two
        # elements of aux2 and check
        # if they are consecutive.
        x = aux2[len(aux2) - 1]
        aux2.pop()
   
        y = aux2[len(aux2) - 1]
        aux2.pop()
   
        if (abs(x - y) != 1):
            result = bool(False)
   
        # Push the elements
        # to queue
        q.put(x)
        q.put(y)
   
    if (len(aux2) == 1):
        q.put(aux2[len(aux2) - 1])
   
    return result 
 
# Driver code
# Pushing elements
# into the queue
q = queue.Queue() 
 
q.put(4)
q.put(5)
q.put(-2)
q.put(-3)
q.put(11)
q.put(10)
q.put(5)
q.put(6)
 
if (pairWiseConsecutive(q)):
    print("Yes")
else:
    print("No")
 
# Printing the original queue
while (not q.empty()):
    print(q.queue[0] ,
          end = " ")
    q.get()
 
# This code is contributed by divyeshrabadiya07

C#




// C# program to check if successive
// pair of numbers in the queue are
// consecutive or not
using System;
using System.Collections.Generic;
     
class GFG
{
 
// Function to check if elements are
// pairwise consecutive in queue
static Boolean pairWiseConsecutive(Queue<int> q)
{
    // Transfer elements of q to aux.
    Stack<int> aux = new Stack<int>();
    while (q.Count != 0)
    {
        aux.Push(q.Peek());
        q.Dequeue();
    }
 
    // Again transfer the
    // elements of aux to aux2
    Stack<int> aux2 = new Stack<int>();
    while (aux.Count != 0)
    {
        aux2.Push(aux.Peek());
        aux.Pop();
    }
 
    // Traverse aux2 and see if
    // elements are pairwise
    // consecutive or not. We also
    // need to make sure that original
    // content is retained.
    Boolean result = true;
    while (aux2.Count > 1)
    {
 
        // Fetch current top two
        // elements of aux2 and check
        // if they are consecutive.
        int x = aux2.Peek();
        aux2.Pop();
 
        int y = aux2.Peek();
        aux2.Pop();
 
        if (Math.Abs(x - y) != 1)
            result = false;
 
        // Push the elements to queue
        q.Enqueue(x);
        q.Enqueue(y);
    }
 
    if (aux2.Count == 1)
        q.Enqueue(aux2.Peek());
 
    return result;
}
 
// Driver code
static public void Main(String[] args)
{
    // Pushing elements into the queue
    Queue<int> q = new Queue<int>();
    q.Enqueue(4);
    q.Enqueue(5);
    q.Enqueue(-2);
    q.Enqueue(-3);
    q.Enqueue(11);
    q.Enqueue(10);
    q.Enqueue(5);
    q.Enqueue(6);
 
    if (pairWiseConsecutive(q))
        Console.WriteLine("Yes");
    else
        Console.WriteLine("No");
 
    // Printing the original queue
    while (q.Count != 0)
    {
        Console.Write(q.Peek() + " ");
        q.Dequeue();
    }
    Console.WriteLine();
 
    }
}
 
// This code is contributed by 29AjayKumar

Output:

Yes
4 5 -2 -3 11 10 5 6 

Time Complexity: O(n), where n is the size of the queue. 
Auxiliary Space: O(n), where n is the size of the stack.

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