Undulating numbers

An undulating number is a number that has only two types of digits and alternate digits are same, i.e., it is of the form “ababab….”. It is sometimes restricted to non-trivial undulating numbers which are required to have at least 3 digits and a is not equal to b.

The first few such numbers are: 101, 121, 131, 141, 151, 161, 171, 181, 191, 202, 212, 232, 242, 252, 262, 272, 282, 292, 303, 313, 323, 343, 353, 363, 373, 383, 393, 404, 414, 424, 434, 454, 464, 474, 484, 494, …
Some higher undulating numbers are: 6363, 80808, 1717171.

  1. For any n >= 3, there are 9 × 9 = 81 non-trivial n-digit undulating numbers, since the first digit can have 9 values (it cannot be 0), and the second digit can have 9 values when it must be different from the first.

Given a number, check if it is Undulating numbers considering the definition of alternating digits, at least 3 digits and adjacent digits not same.

Examples :

Input : n = 121
Output : Yes

Input : n = 1991
Output : No

C++

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// C++ program to check whether a number
// is undulating or not
#include <bits/stdc++.h>
using namespace std;
  
bool isUndulating(string n)
{
    // Considering the definition
    // with restriction that there
    // should be at least 3 digits
    if (n.length() <= 2)
       return false;
  
    // Check if all alternate digits are
    // same or not.
    for (int i = 2; i < n.length(); i++) 
        if (n[i - 2] != n[i]) 
           false;
  
    return true;
}
  
int main()
{
    string n = "1212121";
    if (isUndulating(n))
        cout << "Yes";
    else
        cout << "No";
}

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Java

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// Java program to check whether a number
// is undulating or not
import java.util.*;
  
class GFG {
      
    public static boolean isUndulating(String n)
    {
          
        // Considering the definition
        // with restriction that there
        // should be at least 3 digits
            if (n.length() <= 2)
                return false;
      
        // Check if all alternate digits are
        // same or not.
        for (int i = 2; i < n.length(); i++) 
            if (n.charAt(i-2) != n.charAt(i)) 
                return false;
      
        return true;
    }
      
      
    // Driver code
    public static void main (String[] args)
    {
          
        String n = "1212121";
          
        if (isUndulating(n)==true)
            System.out.println("yes");
        else
            System.out.println("no");
    }
}
  
// This code is contributed by akash1295.

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Python3

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# Python3 program to check whether a 
# number is undulating or not
  
def isUndulating(n):
  
    # Considering the definition
    # with restriction that there
    # should be at least 3 digits
    if (len(n) <= 2):
        return False
  
    # Check if all alternate digits 
    # are same or not.
    for i in range(2, len(n)): 
        if (n[i - 2] != n[i]):
            return False
  
    return True
  
# Driver Code
n = "1212121"
if (isUndulating(n)):
    print("Yes")
else:
    print("No")
  
# This code is contributed by Smitha Dinesh Semwal. 

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C#

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// C# program to check whether a number
// is undulating or not
using System;
  
class GFG {
      
    public static bool isUndulating(string n)
    {
          
        // Considering the definition
        // with restriction that there
        // should be at least 3 digits
            if (n.Length <= 2)
                return false;
      
        // Check if all alternate digits are
        // same or not.
        for (int i = 2; i < n.Length; i++) 
            if (n[i-2] != n[i]) 
                return false;
      
        return true;
    }
      
    // Driver code
    public static void Main ()
    {
          
        string n = "1212121";
          
        if (isUndulating(n)==true)
            Console.WriteLine("yes");
        else
            Console.WriteLine("no");
    }
}
  
// This code is contributed by Vt_m.

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PHP

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<?php
// PHP program to check whether a 
// number is undulating or not
  
function isUndulating($n)
{
      
    // Considering the definition
    // with restriction that there
    // should be at least 3 digits
    if (strlen($n) <= 2)
        return false;
  
    // Check if all alternate 
    // digits are same or not.
    for ($i = 2; $i < strlen($n); $i++) 
        if ($n[$i - 2] != $n[$i]) 
            false;
  
    return true;
}
  
// Driver code
$n = "1212121";
if (isUndulating($n))
    echo("Yes");
else
    echo("No");
  
// This code is contributed by Ajit.
?>

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Output:

Yes


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