Check if Queue Elements are pairwise consecutive

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

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach :

Take a variable n to store size of queue.
Push an element to the queue which acts as marker.
Now, If size of queue is odd, start popping a pair while n > 2. Also, while popping these pairs, check for their difference and decrease n by 2, if there difference is not equal to 1, set flag to false.
If size of queue is even, start popping a pair while n > 1. Also, while popping these pairs, check for their difference and decrease n by 2, if their difference is not equal to 1, set flag to false.
Finally, check flag, if it is true, it means elements in the queue are pairwise sorted, else not.

Below is the implementation of 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) 
{ 
    // Fetching size of queue 
    int n = q.size(); 
  
    // Pushing extra element to the queue 
    // which acts as marker 
    q.push(INT_MIN); 
  
    // Result flag 
    bool result = true; 
  
    // If number of elements in the 
    // queue is odd pop elements while 
    // its size is greater than 2. 
    // Else, pop elements while its 
    // size is greater than 1 
    if (n % 2 != 0) { 
  
        while (n > 2) { 
            int x = q.front(); 
            q.pop(); 
            q.push(x); 
            n--; 
  
            int y = q.front(); 
            q.pop(); 
            q.push(y); 
            n--; 
  
            if (abs(x - y) != 1) { 
                result = false; 
            } 
        } 
  
        // Popping the last element of queue 
        // and pushing it again. 
        // Also, popping the extra element 
        // that we have pushed as marker 
        q.push(q.front()); 
        q.pop(); 
        q.pop(); 
    } 
  
    else { 
        while (n > 1) { 
            int x = q.front(); 
            q.pop(); 
            q.push(x); 
            n--; 
  
            int y = q.front(); 
            q.pop(); 
            q.push(y); 
            n--; 
  
            if (abs(x - y) != 1) { 
                result = false; 
            } 
        } 
  
        // popping the extra element that 
        // we have pushed as marker 
        q.pop(); 
    } 
  
    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); 
    q.push(8); 
  
    if (pairWiseConsecutive(q)) 
        cout << "Yes" << endl; 
    else
        cout << "No" << endl; 
  
    return 0; 
} 

Java

import java.util.LinkedList; 
import java.util.Queue; 
  
// Java program to check if successive  
// pair of numbers in the queue are  
// consecutive or not  
public class GFG { 
  
// Function to check if elements are  
// pairwise consecutive in queue  
    static boolean pairWiseConsecutive(Queue<Integer> q) { 
        // Fetching size of queue  
        int n = q.size(); 
  
        // Pushing extra element to the queue  
        // which acts as marker  
        q.add(Integer.MAX_VALUE); 
  
        // Result flag  
        boolean result = true; 
  
        // If number of elements in the  
        // queue is odd pop elements while  
        // its size is greater than 2.  
        // Else, pop elements while its  
        // size is greater than 1  
        if (n % 2 != 0) { 
  
            while (n > 2) { 
                int x = q.peek(); 
                q.remove(); 
                q.add(x); 
                n--; 
  
                int y = q.peek(); 
                q.remove(); 
                q.add(y); 
                n--; 
  
                if (Math.abs(x - y) != 1) { 
                    result = false; 
                } 
            } 
  
            // Popping the last element of queue  
            // and pushing it again.  
            // Also, popping the extra element  
            // that we have pushed as marker  
            q.add(q.peek()); 
            q.remove(); 
            q.remove(); 
        } else { 
            while (n > 1) { 
                int x = q.peek(); 
                q.remove(); 
                q.add(x); 
                n--; 
  
                int y = q.peek(); 
                q.remove(); 
                q.add(y); 
                n--; 
  
                if (Math.abs(x - y) != 1) { 
                    result = false; 
                } 
            } 
  
            // popping the extra element that  
            // we have pushed as marker  
            q.remove(); 
        } 
  
        return result; 
    } 
  
// Driver program  
    static public void main(String[] args) { 
        // Pushing elements into the queue  
        Queue<Integer> q = new LinkedList<>(); 
        q.add(4); 
        q.add(5); 
        q.add(-2); 
        q.add(-3); 
        q.add(11); 
        q.add(10); 
        q.add(5); 
        q.add(6); 
        q.add(8); 
  
        if (pairWiseConsecutive(q)) { 
            System.out.println("Yes"); 
        } else { 
            System.out.println("No"); 
        } 
  
    } 
} 
// This code is contributed by Rajput-Ji 