Skip to content
Related Articles

Related Articles

To check divisibility of any large number by 999

View Discussion
Improve Article
Save Article
  • Difficulty Level : Medium
  • Last Updated : 05 Aug, 2022
View Discussion
Improve Article
Save Article

You are given an n-digit large number, you have to check whether it is divisible by 999 without dividing or finding modulo of number by 999.

Examples: 

Input : 235764 
Output : Yes

Input : 23576 
Output : No

Since input number may be very large, we cannot use n % 999 to check if a number is divisible by 999 or not, especially in languages like C/C++. The idea is based on following fact.

Recommended Practice

The solutions is based on below fact.

A number is divisible by 999 if sum of its 3-digit-groups (if required groups are formed by appending a 0s at the beginning) is divisible by 999.

Illustration: 

Input : 235764 
Output : Yes
Explanation : Step I - read input : 235, 764
              Step II - 235 + 764 = 999
              As result is 999 then we can 
              conclude that it is divisible by 999.

Input : 1244633121
Output : Yes
Explanation : Step I - read input : 1, 244, 633, 121
              Step II - 001 + 244 + 633 + 121 = 999
              As result is 999 then we can conclude 
              that it is divisible by 999.

Input : 999999999
Output : Yes
Explanation : Step I - read input : 999, 999, 999
              Step II - 999 + 999 + 999 = 2997
              Step III - 997 + 002 = 999
              As result is 999 then we can conclude  
              that it is divisible by 999.

How does this work? 

Let us consider 235764, we can write it as
235764 = 2*105 + 3*104 + 5*103 + 
         7*102 + 6*10 + 4

The idea is based on below observation:
Remainder of 103 divided by 999 is 1
For i > 3, 10i % 999 = 10i-3 % 999 

Let us see how we use above fact.
Remainder of 2*105 + 3*104 + 5*103 + 
7*102 + 6*10 + 4
Remainder with 999 can be written as : 
2*100 + 3*10 + 5*1 + 7*100 + 6*10 + 4 
The above expression is basically sum of
groups of size 3.

Since the sum is divisible by 999, answer is yes.

A simple and efficient method is to take input in form of string (make its length in form of 3*m by adding 0 to left of number if required) and then you have to add the digits in blocks of three from right to left until it become a 3 digit number and if that result is 999 we can say that number is divisible by 999.

As in the case of “divisibility by 9” we check that sum of all digit is divisible by 9 or not, the same thing follows within the case of divisibility by 999. We sum up all 3-digits group from right to left and check whether the final result is 999 or not.

Implementation:
 

C++




// CPP for divisibility of number by 999
#include<bits/stdc++.h>
using namespace std;
 
// function to check divisibility
bool isDivisible999(string num)
{
    int n = num.length();
    if (n == 0 && num[0] == '0')
       return true;
 
    // Append required 0s at the beginning.
    if (n % 3 == 1)
       num = "00" + num;
    if (n % 3 == 2)
       num = "0" + num;
 
    // add digits in group of three in gSum
    int gSum = 0;
    for (int i = 0; i<n; i++)
    {
        // group saves 3-digit group
        int group = 0;
        group += (num[i++] - '0') * 100;
        group += (num[i++] - '0') * 10;
        group += num[i] - '0';
        gSum += group;
    }
 
    // calculate result till 3 digit sum
    if (gSum > 1000)
    {
        num = to_string(gSum);
        n = num.length();
        gSum = isDivisible999(num);
    }
    return (gSum == 999);
}
 
// driver program
int main()
{
    string num = "1998";
    int n = num.length();
    if (isDivisible999(num))
        cout << "Divisible";
    else
        cout << "Not divisible";
    return 0;
}

Java




//Java for divisibility of number by 999
 
class Test
{   
    // Method to check divisibility
    static boolean isDivisible999(String num)
    {
        int n = num.length();
        if (n == 0 && num.charAt(0) == '0')
           return true;
      
        // Append required 0s at the beginning.
        if (n % 3 == 1)
           num = "00" + num;
        if (n % 3 == 2)
           num = "0" + num;
      
        // add digits in group of three in gSum
        int gSum = 0;
        for (int i = 0; i<n; i++)
        {
            // group saves 3-digit group
            int group = 0;
            group += (num.charAt(i++) - '0') * 100;
            group += (num.charAt(i++) - '0') * 10;
            group += num.charAt(i) - '0';
            gSum += group;
        }
      
        // calculate result till 3 digit sum
        if (gSum > 1000)
        {
            num = Integer.toString(gSum);
            n = num.length();
            gSum = isDivisible999(num) ? 1 : 0;
        }
        return (gSum == 999);
    }
     
    // Driver method
    public static void main(String args[])
    {
        String num = "1998";
      
        System.out.println(isDivisible999(num) ? "Divisible" : "Not divisible");
    }
}

Python 3




# Python3 program for divisibility
# of number by 999
 
# function to check divisibility
def isDivisible999(num):
    n = len(num);
    if(n == 0 or num[0] == '0'):
        return true
 
    # Append required 0s at the beginning.
    if((n % 3) == 1):
        num = "00" + num
    if((n % 3) == 2):
        num = "0" + num
 
    # add digits in group of three in gSum    
    gSum = 0
    for i in range(0, n, 3):
         
        # group saves 3-digit group
        group = 0
        group += (ord(num[i]) - 48) * 100
        group += (ord(num[i + 1]) - 48) * 10
        group += (ord(num[i + 2]) - 48)
        gSum += group
 
    # calculate result till 3 digit sum    
    if(gSum > 1000):
        num = str(gSum)
        n = len(num)
        gSum = isDivisible999(num)
    return (gSum == 999)
 
# Driver code
if __name__=="__main__":
    num = "1998"
    n = len(num)
    if(isDivisible999(num)):
        print("Divisible")
    else:
        print("Not divisible")
         
# This code is contributed
# by Sairahul Jella

C#




// C# code for divisibility of number by 999
 
using System;
class Test
{
    // Method to check divisibility
    static bool isDivisible999(String num)
    {
        int n = num.Length;
        if (n == 0 && num[0] == '0')
        return true;
     
        // Append required 0s at the beginning.
        if (n % 3 == 1)
        num = "00" + num;
        if (n % 3 == 2)
        num = "0" + num;
     
        // add digits in group of three in gSum
        int gSum = 0;
        for (int i = 0; i<n; i++)
        {
            // group saves 3-digit group
            int group = 0;
            group += (num[i++] - '0') * 100;
            group += (num[i++] - '0') * 10;
            group += num[i] - '0';
            gSum += group;
        }
     
        // calculate result till 3 digit sum
        if (gSum > 1000)
        {
            num = Convert.ToString(gSum);
            n = num.Length ;
            gSum = isDivisible999(num) ? 1 : 0;
        }
        return (gSum == 999);
    }
     
    // Driver method
    public static void Main()
    {
        String num = "1998";
     
        Console.WriteLine(isDivisible999(num) ? "Divisible" : "Not divisible");
    }
    // This code is contributed by Ryuga
}

PHP




<?php
// PHP for divisibility of number by 999
 
// function to check divisibility
function isDivisible999($num)
{
    $n = strlen($num);
    if ($n == 0 && $num[0] == '0')
    return true;
 
    // Append required 0s at the beginning.
    if ($n % 3 == 1)
        $num = "00" . $num;
    if ($n % 3 == 2)
        $num = "0" . $num;
 
    // add digits in group of three in gSum
    $gSum = 0;
    for ($i = 0; $i < $n; $i += 3)
    {
        // group saves 3-digit group
        $group = 0;
        $group += (ord($num[$i]) - 48) * 100;
        $group += (ord($num[$i + 1]) - 48) * 10;
        $group += (ord($num[$i + 2]) - 48);
        $gSum += $group;
    }
     
    // calculate result till 3 digit sum
    if ($gSum > 1000)
    {
        $num = strval($gSum);
        $n = strlen($num);
        $gSum = isDivisible999($num);
    }
    return ($gSum == 999);
}
 
// Driver Code
$num = "1998";
if (isDivisible999($num))
    echo "Divisible";
else
    echo "Not divisible";
 
// This code is contributed by mits
?>

Javascript




<script>
// Javascript for divisibility of number by 999
 
// function to check divisibility
function isDivisible999(num)
{
    let n = num.length;
    if (n == 0 && num[0] == '0')
    return true;
 
    // Append required 0s at the beginning.
    if (n % 3 == 1)
        num = "00" + num;
    if (n % 3 == 2)
        num = "0" + num;
 
    // add digits in group of three in gSum
    let gSum = 0;
    for (let i = 0; i < n; i += 3)
    {
        // group saves 3-digit group
        group = 0;
        group += (num.charCodeAt(i) - 48) * 100;
        group += (num.charCodeAt(i + 1) - 48) * 10;
        group += (num.charCodeAt(i + 2) - 48);
        gSum += group;
    }
     
    // calculate result till 3 digit sum
    if (gSum > 1000)
    {
        num = String(gSum);
        n = strlen(num);
        gSum = isDivisible999(num);
    }
    return (gSum == 999);
}
 
// Driver Code
let num = "1998";
if (isDivisible999(num))
    document.write("Divisible");
else
    document.write("Not divisible");
 
// This code is contributed by _saurabh_jaiswal.
</script>

Output

Divisible

Time complexity : O(n) 
Auxiliary Space : O(1)

Method: Checking given any number is divisible by 999 or not by using modulo division operator “%”.  

Implementation:

C++




#include <iostream>
using namespace std;
int main()
{
    //input
    long long int n=235764;
      
      
    // finding given number is divisible by 999 or not
    if (n%999==0)
    {
        cout << "Yes";
    }
    else
    {
        cout << "No";
    }
    
    return 0;
}
 
// This code is contributed by satwik4409.

Java




/*package whatever //do not write package name here */
import java.io.*;
 
class GFG {
  public static void main (String[] args) {
 
    // input
    long n = 235764;
 
    // the above input can also be given as n=input() -> taking input from user
    // finding given number is divisible by 999 or not
    if (n % 999 == 0)
      System.out.println("Yes");
    else
      System.out.println("No");
 
  }
}
 
// This code is contributed by ksrikanth0498.

Python3




# Python code
# To check whether the given number is divisible by 999 or not
 
#input
n=235764
# the above input can also be given as n=input() -> taking input from user
# finding given number is divisible by 999 or not
if int(n)%999==0:
  print("Yes")
else:
  print("No")
   
  # this code is contributed by gangarajula laxmi

C#




// C# code
// To check whether the given number is divisible by 999 or not
using System;
 
public class GFG{
 
    static public void Main ()
    {
       
       // input
       long n = 235764;
       
      // the above input can also be given as n=input() -> taking input from user
        // finding given number is divisible by 999 or not
       if (n % 999 == 0)
            Console.Write("Yes");
        else
            Console.Write("No");
    }
}
 
// This code is contributed by ksrikanth0498

Javascript




<script>
        // JavaScript code for the above approach
        //input
        let n = 235764
        // the above input can also be given as n=input() -> taking input from user
        // finding given number is divisible by 999 or not
        if (n % 999 == 0)
            document.write("Yes")
        else
            document.write("No")
    // This code is contributed by Potta Lokesh
    </script>

Output

Yes

Time complexity : O(log(n)), for small numbers.

For large integers, Python division (and modulo) use an O(n^2) algorithm. Multiplication uses the Karatsuba multiplication which is O(n^1.585) but division uses basic “grade-school” division.

Auxiliary Space : O(1)

More Divisibility Algorithms.
This article is contributed by Shivam Pradhan (anuj_charm). If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks. 


My Personal Notes arrow_drop_up
Recommended Articles
Page :

Start Your Coding Journey Now!