Demlo number (Square of 11…1)

Given a number of the form 11..1 such that number of digits in it is smaller than 10, find square of the number.
Examples:

Input : 111111
Output : 12345654321

Input : 1111
Output : 1234321

Squares of 11…1 (where length is smaller than 10) are called Demlo numbers. A demlo number is number which consist of 1, 2, 3….n, n-1, n-2, …..1. 
Demlo numbers are: 

1 = 1
11 * 11 = 121
111 * 111 = 12321
1111 * 1111 = 1234321

To find demlo number, first we find append n numbers which are increasing and then append numbers which are decreasing.

C++

// CPP program to print DemloNumber
#include <bits/stdc++.h>
using namespace std;

// To return demlo number. This function assumes
// that the length of str is smaller than 10.
string printDemlo(string str)
{
    int len = str.length();
    string res = "";

    // Add numbers to res upto size
    // of str and then add number
    // reverse to it
    for (int i = 1; i <= len; i++)
        res += char(i + '0');

    for (int i = len - 1; i >= 1; i--)
        res += char(i + '0');

    return res;
}

// Driver program to test printDemlo()
int main()
{
    string str = "111111";
    cout << printDemlo(str);
    return 0;
}

Java

// Java program to print DemloNumber
public class Main {

    // To return demlo number. This function assumes
    // that the length of str is smaller than 10.
    static String printDemlo(String str)
    {
        int len = str.length();
        String res = "";

        // Add numbers to res upto size
        // of str and then add number
        // reverse to it
        for (int i = 1; i <= len; i++)
            res += Integer.toString(i);

        for (int i = len - 1; i >= 1; i--)
            res += Integer.toString(i);

        return res;
    }

    // Driver program to test printDemlo()
    public static void main(String[] args)
    {
        String str = "111111";
        System.out.println(printDemlo(str));
    }
}

Python3

# Python program to print Demlo Number

# To return demlo number
# Length of s is smaller than 10
def printDemlo(s):
    l = len(s)
    res = ""

    # Add numbers to res upto size
    # of s then add in reverse

    for i in range(1,l+1):
        res = res + str(i)

    for i in range(l-1,0,-1):
        res = res + str(i)

    return res


# Driver Code
s = "111111"
print (printDemlo(s))

# Contributed by Harshit Agrawal

C#

// C# program to print DemloNumber
using System;
public class GFG {

    // To return demlo number. This function assumes
    // that the length of str is smaller than 10.
    static String printDemlo(String str)
    {
        int len = str.Length;
        String res = "";

        // Add numbers to res upto size
        // of str and then add number
        // reverse to it
        for (int i = 1; i <= len; i++)
            res += i.ToString();

        for (int i = len - 1; i >= 1; i--)
            res += i.ToString();

        return res;
    }

    // Driver program to test printDemlo()
    public static void Main()
    {
        String str = "111111";
        Console.WriteLine(printDemlo(str));
    }
}
// This code is contributed by mits

PHP

<?php
// PHP program to print DemloNumber

// To return demlo number. This function
// assumes that the length of str is
// smaller than 10.
function printDemlo($str)
{
    $len = strlen($str);
    $res = "";

    // Add numbers to res upto size
    // of str and then add number
    // reverse to it
    for ($i = 1; $i <= $len; $i++)
        $res .= chr($i + 48);

    for ($i = $len - 1; $i >= 1; $i--)
        $res .= chr($i + 48);

    return $res;
}

// Driver Code
$str = "111111";
echo printDemlo($str);

// This code is contributed by mits
?>

Javascript

<script>

// Javascript program to print DemloNumber

    // To return demlo number. This function assumes
    // that the length of str is smaller than 10.
    function printDemlo(str)
    {
        let len = str.length;
        let res = "";

        // Add numbers to res upto size
        // of str and then add number
        // reverse to it
        for (let i = 1; i <= len; i++)
            res += i.toString();

        for (let i = len - 1; i >= 1; i--)
            res += i.toString();

        return res;
    }

// driver program
        let str = "111111";
        document.write(printDemlo(str));

  // This code is contributed by susmitakundugoaldanga.
</script>

Output:

12345654321

Time complexity: O(log N) where N is the length of string “str” of number n

Auxiliary space: O(1) because it is using constant space

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