n-th number whose sum of digits is ten

Given an integer value n, find out the n-th positive integer whose sum is 10. 

Examples:

Input: n = 2
Output: 28
The first number with sum of digits as
10 is 19. Second number is 28.

Input: 15
Output: 154

Method 1 (Simple):
We traverse through all numbers. For every number, we find the sum of digits. We stop when we find the n-th number with the sum of digits as 10.

C++

// Simple CPP program to find n-th number
// with sum of digits as 10.
#include <bits/stdc++.h>
using namespace std;

int findNth(int n)
{
    int count = 0;

    for (int curr = 1;; curr++) {

        // Find sum of digits in current no.
        int sum = 0;
        for (int x = curr; x > 0; x = x / 10)
            sum = sum + x % 10;

        // If sum is 10, we increment count
        if (sum == 10)
            count++;

        // If count becomes n, we return current
        // number.
        if (count == n)
            return curr;
    }
    return -1;
}

int main()
{
    printf("%d\n", findNth(5));
    return 0;
}

Java

// Java program to find n-th number
// with sum of digits as 10.

import java.util.*;
import java.lang.*;

public class GFG {
    public static int findNth(int n)
    {
        int count = 0;
        for (int curr = 1;; curr++) {

            // Find sum of digits in current no.
            int sum = 0;
            for (int x = curr; x > 0; x = x / 10)
                sum = sum + x % 10;

            // If sum is 10, we increment count
            if (sum == 10)
                count++;

            // If count becomes n, we return current
            // number.
            if (count == n)
                return curr;
        }
    }

    public static void main(String[] args)
    {
        System.out.print(findNth(5));
    }
}

// Contributed by _omg

Python3

# Python3 program to find n-th number
# with sum of digits as 10.
import itertools

# function to find required number
def findNth(n):

    count = 0

    for curr in itertools.count():
        # Find sum of digits in current no.
        sum = 0
        x = curr
        while(x):
            sum = sum + x % 10
            x = x // 10

        # If sum is 10, we increment count
        if (sum == 10):
            count = count + 1

        # If count becomes n, we return current
        # number.
        if (count == n):
            return curr

    return -1

# Driver program
if __name__=='__main__':
    print(findNth(5))

# This code is contributed by
# Sanjit_Prasad

C#

// C# program to find n-th number
// with sum of digits as 10.
using System;

class GFG {
    public static int findNth(int n)
    {
        int count = 0;
        for (int curr = 1;; curr++) {

            // Find sum of digits in current no.
            int sum = 0;
            for (int x = curr; x > 0; x = x / 10)
                sum = sum + x % 10;

            // If sum is 10, we increment count
            if (sum == 10)
                count++;

            // If count becomes n, we
            // return current number.
            if (count == n)
                return curr;
        }
    }

    // Driver Code
    static public void Main()
    {
        Console.WriteLine(findNth(5));
    }
}

// This code is contributed
// by Sach_Code

Javascript

<script>

// Simple JavaScript program to find n-th number
// with sum of digits as 10.

function findNth(n)
{
    let count = 0;

    for (let curr = 1;; curr++) {

        // Find sum of digits in current no.
        let sum = 0;
        for (let x = curr; x > 0; x = Math.floor(x / 10))
            sum = sum + x % 10;

        // If sum is 10, we increment count
        if (sum == 10)
            count++;

        // If count becomes n, we return current
        // number.
        if (count == n)
            return curr;
    }
    return -1;
}


    document.write(findNth(5));


// This code is contributed by Surbhi Tyagi.

</script>

PHP

<?php
// Simple PHP program to find n-th
// number with sum of digits as 10.
function findNth($n)
{
    $count = 0;

    for ($curr = 1; ; $curr++)
    {

        // Find sum of digits in
        // current no.
        $sum = 0;
        for ($x = $curr;
             $x > 0; $x = $x / 10)
            $sum = $sum + $x % 10;

        // If sum is 10, we increment
        // count
        if ($sum == 10)
            $count++;

        // If count becomes n, we return
        // current number.
        if ($count == $n)
            return $curr;
    }
    return -1;
}

// Driver Code
echo findNth(5);

// This code is contributed by Sach .
?>

Output

55

Time Complexity: O(N*log₁₀(N))
Auxiliary Space: O(1)

Method 2 (Efficient): 

If we take a closer look, we can notice that all multiples of 9 are present in arithmetic progression 19, 28, 37, 46, 55, 64, 73, 82, 91, 100, 109,… However, there are numbers in the above series whose sum of digits is not 10, for example, 100. So instead of checking one by one, we start with 19 and increment by 9.

C++

// Simple CPP program to find n-th number
// with sum of digits as 10.
#include <bits/stdc++.h>
using namespace std;

int findNth(int n)
{
    int count = 0;

    for (int curr = 19;; curr += 9) {

        // Find sum of digits in current no.
        int sum = 0;
        for (int x = curr; x > 0; x = x / 10)
            sum = sum + x % 10;

        // If sum is 10, we increment count
        if (sum == 10)
            count++;

        // If count becomes n, we return current
        // number.
        if (count == n)
            return curr;
    }
    return -1;
}

int main()
{
    printf("%d\n", findNth(5));
    return 0;
}

Java

// Java program to find n-th number
// with sum of digits as 10.

import java.util.*;
import java.lang.*;

public class GFG {
    public static int findNth(int n)
    {
        int count = 0;

        for (int curr = 19;; curr += 9) {

            // Find sum of digits in current no.
            int sum = 0;
            for (int x = curr; x > 0; x = x / 10)
                sum = sum + x % 10;

            // If sum is 10, we increment count
            if (sum == 10)
                count++;

            // If count becomes n, we return current
            // number.
            if (count == n)
                return curr;
        }
    }

    public static void main(String[] args)
    {
        System.out.print(findNth(5));
    }
}

// Contributed by _omg

Python3

# Python3 program to find n-th
# number with sum of digits as 10.
def findNth(n):
    count = 0;

    curr = 19;

    while (True):

        # Find sum of digits in
        # current no.
        sum = 0;
        x = curr;
        while (x > 0):
            sum = sum + x % 10;
            x = int(x / 10);

        # If sum is 10, we increment
        # count
        if (sum == 10):
            count+= 1;

        # If count becomes n, we return
        # current number.
        if (count == n):
            return curr;

        curr += 9;

    return -1;

# Driver Code
print(findNth(5));

# This code is contributed
# by mits

C#

// C# program to find n-th number
// with sum of digits as 10.
using System;

class GFG {
    public static int findNth(int n)
    {
        int count = 0;

        for (int curr = 19;; curr += 9) {

            // Find sum of digits in
            // current no.
            int sum = 0;
            for (int x = curr;
                 x > 0; x = x / 10)
                sum = sum + x % 10;

            // If sum is 10, we increment
            // count
            if (sum == 10)
                count++;

            // If count becomes n, we return
            // current number.
            if (count == n)
                return curr;
        }
    }

    // Driver Code
    static public void Main()
    {
        Console.WriteLine(findNth(5));
    }
}

// This code is contributed
// by Sach_Code

Javascript

<script>

// Simple Javascript program to find n-th
// number with sum of digits as 10.
function findNth(n)
{
    let count = 0;

    for (let curr = 19; ;curr += 9)
    {

        // Find sum of digits in
        // current no.
        let sum = 0;
        for (let x = curr; x > 0;
             x = parseInt(x / 10))
            sum = sum + x % 10;

        // If sum is 10, we increment
        // count
        if (sum == 10)
            count++;

        // If count becomes n, we return
        // current number.
        if (count == n)
            return curr;
    }
    return -1;
}

// Driver Code
document.write(findNth(5));

// This code is contributed
// by gfgking
</script>

PHP

<?php
// Simple PHP program to find n-th
// number with sum of digits as 10.
function findNth($n)
{
    $count = 0;

    for ($curr = 19; ;$curr += 9)
    {

        // Find sum of digits in
        // current no.
        $sum = 0;
        for ($x = $curr; $x > 0;
             $x = (int)$x / 10)
            $sum = $sum + $x % 10;

        // If sum is 10, we increment
        // count
        if ($sum == 10)
            $count++;

        // If count becomes n, we return
        // current number.
        if ($count == $n)
            return $curr;
    }
    return -1;
}

// Driver Code
echo findNth(5);

// This code is contributed
// by Sach_Code
?>

Output

55

Time Complexity: O(N*log₁₀(N))
Auxiliary Space: O(1)