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Composite numbers with digit sum 1

  • Last Updated : 08 Mar, 2021

Given a range [L, R], the task is to find all the numbers from the range which are composite as well as the eventual sum of their digits is 1.
Examples: 
 

Input: L = 10, R = 100 
Output: 10 28 46 55 64 82 91 100 
10 = 1 + 0 = 1 
28 = 2 + 8 = 10 = 1 + 0 = 1 
… 
91 = 9 + 1 = 10 = 1 + 0 = 1 
100 = 1 + 0 + 0 = 1
Input: L = 250, R = 350 
Output: 253 262 280 289 298 316 325 334 343 
 

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Approach: For every number in the range check if the number is composite i.e. it has a divisor other than 1 and the number itself. If the current number is a composite number then keep on calculating the sum of its digits until the number is reduced to a single digit, if this digit is 1 then the chosen number is a valid number.
Below is the implementation of the above approach:
 

C++




// C++ implementation of the above approach
#include <iostream>
using namespace std;
 
// Function that returns true if number n
// is a composite number
bool isComposite(int n)
{
    // Corner cases
    if (n <= 1)
        return false;
    if (n <= 3)
        return false;
 
    // This is checked so that we can skip
    // middle five numbers in below loop
    if (n % 2 == 0 || n % 3 == 0)
        return true;
 
    for (int i = 5; i * i <= n; i = i + 6)
        if (n % i == 0 || n % (i + 2) == 0)
            return true;
 
    return false;
}
 
// Function that returns true if the eventual
// digit sum of number nm is 1
bool isDigitSumOne(int nm)
{
 
    // Loop till the sum is not single digit number
    while (nm > 9) {
 
        // Intitialize the sum as zero
        int sum_digit = 0;
 
        // Find the sum of digits
        while (nm > 0) {
            int digit = nm % 10;
            sum_digit = sum_digit + digit;
            nm = nm / 10;
        }
        nm = sum_digit;
    }
 
    // If sum is eventually 1
    if (nm == 1)
        return true;
    else
        return false;
}
 
// Function to print the required numbers
// from the given range
void printValidNums(int l, int r)
{
    for (int i = l; i <= r; i++) {
 
        // If i is one of the required numbers
        if (isComposite(i) && isDigitSumOne(i))
            cout << i << " ";
    }
}
 
// Driver code
int main(void)
{
    int l = 10, r = 100;
 
    printValidNums(l, r);
 
    return 0;
}

Java




// Java implementation of the above approach
public class GFG {
 
    // Function that returns true if number n
    // is a composite number
    static boolean isComposite(int n)
    {
        // Corner cases
        if (n <= 1)
            return false;
        if (n <= 3)
            return false;
 
        // This is checked so that we can skip
        // middle five numbers in below loop
        if (n % 2 == 0 || n % 3 == 0)
            return true;
 
        for (int i = 5; i * i <= n; i = i + 6)
            if (n % i == 0 || n % (i + 2) == 0)
                return true;
 
        return false;
    }
 
    // Function that returns true if the eventual
    // digit sum of number nm is 1
    static boolean isDigitSumOne(int nm)
    {
 
        // Loop till the sum is not single
        // digit number
        while (nm > 9) {
 
            // Intitialize the sum as zero
            int sum_digit = 0;
 
            // Find the sum of digits
            while (nm > 0) {
                int digit = nm % 10;
                sum_digit = sum_digit + digit;
                nm = nm / 10;
            }
            nm = sum_digit;
        }
 
        // If sum is eventually 1
        if (nm == 1)
            return true;
        else
            return false;
    }
 
    // Function to print the required numbers
    // from the given range
    static void printValidNums(int l, int r)
    {
        for (int i = l; i <= r; i++) {
 
            // If i is one of the required numbers
            if (isComposite(i) && isDigitSumOne(i))
                System.out.print(i + " ");
        }
    }
 
    // Driver code
    public static void main(String arg[])
    {
        int l = 10, r = 100;
        printValidNums(l, r);
    }
}

Python3




# Python3 implementation of the approach
 
# Function that returns true if number n
# is a composite number
def isComposite(n):
   
    # Corner cases
    if (n <= 1):
        return False
    if (n <= 3):
        return False
   
    # This is checked so that we can skip 
    # middle five numbers in below loop
    if (n % 2 == 0 or n % 3 == 0):
        return True
    i = 5
    while(i * i <= n):
           
        if (n % i == 0 or n % (i + 2) == 0):
            return True
        i = i + 6
           
    return False
 
# Function that returns true if the eventual
# digit sum of number nm is 1
def isDigitSumOne(nm) :
     
    # Loop till the sum is not single
    # digit number
    while(nm>9) :
         
        # Intitialize the sum as zero
        sum_digit = 0
         
        # Find the sum of digits
        while(nm != 0) :
            digit = nm % 10
            sum_digit = sum_digit + digit
            nm = nm // 10
        nm = sum_digit
     
    # If sum is eventually 1
    if(nm == 1):
        return True
    else:
        return False
         
# Function to print the required numbers
# from the given range
def printValidNums(m, n ):
    for i in range(m, n + 1):
         
        # If i is one of the required numbers
        if(isComposite(i) and isDigitSumOne(i)) :
            print(i, end =" ")
 
# Driver code
l = 10
r = 100
printValidNums(m, n)

C#




// C# implementation of the above approach
using System;
 
class GFG
{
     
    // Function that returns true if number n
    // is a composite number
    static bool isComposite(int n)
    {
         
        // Corner cases
        if (n <= 1)
            return false;
        if (n <= 3)
            return false;
 
        // This is checked so that we can skip
        // middle five numbers in below loop
        if (n % 2 == 0 || n % 3 == 0)
            return true;
 
        for (int i = 5; i * i <= n; i = i + 6)
            if (n % i == 0 || n % (i + 2) == 0)
                return true;
 
        return false;
    }
 
    // Function that returns true if the
    // eventual digit sum of number nm is 1
    static bool isDigitSumOne(int nm)
    {
 
        // Loop till the sum is not single
        // digit number
        while (nm > 9)
        {
 
            // Intitialize the sum as zero
            int sum_digit = 0;
 
            // Find the sum of digits
            while (nm > 0)
            {
                int digit = nm % 10;
                sum_digit = sum_digit + digit;
                nm = nm / 10;
            }
            nm = sum_digit;
        }
 
        // If sum is eventually 1
        if (nm == 1)
            return true;
        else
            return false;
    }
 
    // Function to print the required numbers
    // from the given range
    static void printValidNums(int l, int r)
    {
        for (int i = l; i <= r; i++)
        {
 
            // If i is one of the required numbers
            if (isComposite(i) && isDigitSumOne(i))
                Console.Write(i + " ");
        }
    }
 
    // Driver code
    static public void Main ()
    {
        int l = 10, r = 100;
        printValidNums(l, r);
    }
}
 
// This code is contributed by jit_t

PHP




<?php
// PHP implementation of the above approach
 
// Function that returns true if number n
// is a composite number
function isComposite($n)
{
    // Corner cases
    if ($n <= 1)
        return false;
    if ($n <= 3)
        return false;
 
    // This is checked so that we can skip
    // middle five numbers in below loop
    if ($n % 2 == 0 || $n % 3 == 0)
        return true;
 
    for ($i = 5; $i * $i <= $n; $i = $i + 6)
        if ($n % $i == 0 || $n % ($i + 2) == 0)
            return true;
 
    return false;
}
 
// Function that returns true if the eventual
// digit sum of number nm is 1
function isDigitSumOne($nm)
{
 
    // Loop till the sum is not single
    // digit number
    while ($nm > 9)
    {
 
        // Intitialize the sum as zero
        $sum_digit = 0;
 
        // Find the sum of digits
        while ($nm > 0)
        {
            $digit = $nm % 10;
            $sum_digit = $sum_digit + $digit;
            $nm = floor($nm / 10);
        }
        $nm = $sum_digit;
    }
 
    // If sum is eventually 1
    if ($nm == 1)
        return true;
    else
        return false;
}
 
// Function to print the required numbers
// from the given range
function printValidNums($l, $r)
{
    for ($i = $l; $i <= $r; $i++)
    {
 
        // If i is one of the required numbers
        if (isComposite($i) && isDigitSumOne($i))
            echo $i, " ";
    }
}
 
// Driver code
$l = 10; $r = 100;
 
printValidNums($l, $r);
 
// This code is contributed by Ryuga
?>

Javascript




<script>
 
// Javascript implementation of the above approach
 
// Function that returns true if number n
// is a composite number
function isComposite(n)
{
    // Corner cases
    if (n <= 1)
        return false;
    if (n <= 3)
        return false;
 
    // This is checked so that we can skip
    // middle five numbers in below loop
    if (n % 2 == 0 || n % 3 == 0)
        return true;
 
    for (let i = 5; i * i <= n; i = i + 6)
        if (n % i == 0 || n % (i + 2) == 0)
            return true;
 
    return false;
}
 
// Function that returns true if the eventual
// digit sum of number nm is 1
function isDigitSumOne(nm)
{
 
    // Loop till the sum is not single digit number
    while (nm > 9) {
 
        // Intitialize the sum as zero
        let sum_digit = 0;
 
        // Find the sum of digits
        while (nm > 0) {
            let digit = nm % 10;
            sum_digit = sum_digit + digit;
            nm = Math.floor(nm / 10);
        }
        nm = sum_digit;
    }
 
    // If sum is eventually 1
    if (nm == 1)
        return true;
    else
        return false;
}
 
// Function to print the required numbers
// from the given range
function printValidNums(l, r)
{
    for (let i = l; i <= r; i++) {
 
        // If i is one of the required numbers
        if (isComposite(i) && isDigitSumOne(i))
            document.write(i + " ");
    }
}
 
// Driver code
 
    let l = 10, r = 100;
 
    printValidNums(l, r);
 
     
// This code is contributed by Mayank Tyagi
 
</script>
Output: 
10 28 46 55 64 82 91 100

 

Optimizations : We can precompute composite numbers using Sieve Algorithms.
 




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