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To check a number is palindrome or not without using any extra space

  • Difficulty Level : Medium
  • Last Updated : 06 May, 2021

Given a number ‘n’ and our goal is to find out it is palindrome or not without using 
any extra space. We can’t make a new copy of number .
Examples: 
 

Input  : 2332
Output : Yes it is Palindrome.
Explanation:
original number = 2332
reversed number = 2332
Both are same hence the number is palindrome.

Input :1111
Output :Yes it is Palindrome.

Input : 1234
Output : No not Palindrome.

 

A recursive solution is discussed in below post. 
Check if a number is Palindrome
In this post a different solution is discussed. 
1) We can compare the first digit and the last digit, then we repeat the process. 
2) For the first digit, we need the order of the number. Say, 12321. Dividing this by 10000 would get us the leading 1. The trailing 1 can be retrieved by taking the mod with 10. 
3 ) Now, to reduce this to 232. 

(12321 % 10000)/10 = (2321)/10 = 232 

4 ) And now, the 10000 would need to be reduced by a factor of 100. 
Here is the implementation of the above algorithm : 
 

C++




// C++ program to find number is palindrome
// or not without using any extra space
#include <bits/stdc++.h>
using namespace std;
bool isPalindrome(int);
 
bool isPalindrome(int n)
{  
    // Find the appropriate divisor
    // to extract the leading digit
    int divisor = 1;
    while (n / divisor >= 10)
        divisor *= 10;
 
    while (n != 0)
    {
        int leading = n / divisor;
        int trailing = n % 10;
 
        // If first and last digit
        // not same return false
        if (leading != trailing) 
            return false;
 
        // Removing the leading and trailing
        // digit from number
        n = (n % divisor) / 10;
 
        // Reducing divisor by a factor
        // of 2 as 2 digits are dropped
        divisor = divisor / 100;
    }
    return true;
}
 
// Driver code
int main()
{
    isPalindrome(1001) ? cout << "Yes, it is Palindrome" :
    cout << "No, not Palindrome";
    return 0;
}

Java




// Java program to find number is palindrome
// or not without using any extra space
public class GFG
{     
    static boolean isPalindrome(int n)
    {  
        // Find the appropriate divisor
        // to extract the leading digit
        int divisor = 1;
        while (n / divisor >= 10)
            divisor *= 10;
      
        while (n != 0)
        {
            int leading = n / divisor;
            int trailing = n % 10;
      
            // If first and last digit
            // not same return false
            if (leading != trailing) 
                return false;
      
            // Removing the leading and trailing
            // digit from number
            n = (n % divisor) / 10;
      
            // Reducing divisor by a factor
            // of 2 as 2 digits are dropped
            divisor = divisor / 100;
        }
        return true;
    }
      
    // Driver code
    public static void main(String args[])
    {
        if(isPalindrome(1001))
            System.out.println("Yes, it is Palindrome");
        else
            System.out.println("No, not Palindrome");
    }
}
// This code is contributed by Sumit Ghosh

Python3




# Python program to find number
# is palindrome or not without
# using any extra space
 
# Function to check if given number
# is palindrome or not without
# using the extra space
def isPalindrome(n):
 
    # Find the appropriate divisor
    # to extract the leading digit
    divisor = 1
    while (n / divisor >= 10):
        divisor *= 10
 
    while (n != 0):
         
        leading = n // divisor
        trailing = n % 10
         
        # If first and last digit
        # not same return false
        if (leading != trailing):
            return False
         
        # Removing the leading and
        # trailing digit from number
        n = (n % divisor)//10
         
        # Reducing divisor by a factor
        # of 2 as 2 digits are dropped
        divisor = divisor/100
         
    return True
 
# Driver code
if(isPalindrome(1001)):
    print('Yes, it is palindrome')
else:
    print('No, not palindrome')
 
# This code is contributed by Danish Raza

C#




// C# program to find number
// is palindrome or not without
// using any extra space
using System;
 
class GFG
{
    static bool isPalindrome(int n)
    {
        // Find the appropriate
        // divisor to extract
        // the leading digit
        int divisor = 1;
        while (n / divisor >= 10)
            divisor *= 10;
     
        while (n != 0)
        {
            int leading = n / divisor;
            int trailing = n % 10;
     
            // If first and last digit
            // not same return false
            if (leading != trailing)
                return false;
     
            // Removing the leading and
            // trailing digit from number
            n = (n % divisor) / 10;
     
            // Reducing divisor by
            // a factor of 2 as 2
            // digits are dropped
            divisor = divisor / 100;
        }
        return true;
    }
     
    // Driver code
    static public void Main ()
    {
        if(isPalindrome(1001))
            Console.WriteLine("Yes, it " +
                         "is Palindrome");
        else
            Console.WriteLine("No, not " +
                            "Palindrome");
    }
}
 
// This code is contributed by m_kit

PHP




<?php
// PHP program to find
// number is palindrome
// or not without using
// any extra space
 
function isPalindrome($n)
{
    // Find the appropriate divisor
    // to extract the leading digit
    $divisor = 1;
    while ($n / $divisor >= 10)
        $divisor *= 10;
 
    while ($n != 0)
    {
        $leading = floor($n / $divisor);
        $trailing = $n % 10;
 
        // If first and last digit
        // not same return false
        if ($leading != $trailing)
            return false;
 
        // Removing the leading and
        // trailing digit from number
        $n = ($n % $divisor) / 10;
 
        // Reducing divisor by a
        // factor of 2 as 2 digits
        // are dropped
        $divisor = $divisor / 100;
    }
    return true;
}
 
// Driver code
if(isPalindrome(1001) == true)
echo "Yes, it is Palindrome" ;
else
 
echo "No, not Palindrome";
 
// This code is contributed by ajit
?>

Javascript




<script>
// javascript program to find number is palindrome
// or not without using any extra space
 
    function isPalindrome(n) {
        // Find the appropriate divisor
        // to extract the leading digit
        var divisor = 1;
        while (parseInt(n / divisor) >= 10)
            divisor *= 10;
 
        while (n != 0) {
            var leading = parseInt(n / divisor);
            var trailing = n % 10;
 
            // If first and last digit
            // not same return false
            if (leading != trailing)
                return false;
 
            // Removing the leading and trailing
            // digit from number
            n = parseInt((n % divisor) / 10);
 
            // Reducing divisor by a factor
            // of 2 as 2 digits are dropped
            divisor = divisor / 100;
        }
        return true;
    }
 
    // Driver code
     
        if (isPalindrome(1001))
            document.write("Yes, it is Palindrome");
        else
            document.write("No, not Palindrome");
 
// This code is contributed by todaysgaurav
</script>

Output: 
 

Yes, it is Palindrome

This article is contributed by Abhijit Shankhdhar. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
 

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