Find the largest N digit multiple of N

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Given a number N, the task is to find the largest N-digit multiple of N.
Examples:

Input: N = 2
Output: 98
Explanation:
98 is the largest multiple of 2 and is of 2 digits.
Input: N = 3
Output: 999
Explanation:
999 is the largest multiple of 3 and is of 3 digits.

Approach: The idea is to make an observation.

If we observe carefully, a series will be formed as 9, 98, 999, 9996, 99995, …
In the above series, the N-th term can be calculated as:

$N*\lfloor \frac{10^N-1}{N} \rfloor$

Therefore, the number N is taken as the input and the above formula is implemented.

Below is the implementation of the above approach:

C++

// C++ program to find largest multiple
// of N containing N digits
#include <iostream>
#include <math.h>
using namespace std;
 
// Function to find the largest 
// N digit multiple of N
 
void smallestNumber(int N)
{
    cout << N * floor((pow(10, N) - 1) / N);
}
 
// Driver code
int main()
{
    int N = 2;
    smallestNumber(N);
 
    return 0;
}

Java

// Java program to find largest multiple
// of N containing N digits
import java.util.*;
class GFG{
 
// Function to find the largest 
// N digit multiple of N
static void smallestNumber(int N)
{
    System.out.print(N * Math.floor((
                         Math.pow(10, N) - 1) / N));
}
 
// Driver code
public static void main(String args[])
{
    int N = 2;
    smallestNumber(N);
}
}
 
// This code is contributed by Nidhi_biet

Python3

# Python3 program to find largest multiple
# of N containing N digits
from math import floor
 
# Function to find the largest
# N digit multiple of N
def smallestNumber(N):
    print(N * floor((pow(10, N) - 1) / N))
 
# Driver code
if __name__ == '__main__':
    N = 2
    smallestNumber(N)
 
# This code is contributed by Mohit Kumar

C#

// C# program to find largest multiple
// of N containing N digits
using System;
class GFG{
 
// Function to find the largest 
// N digit multiple of N
static void smallestNumber(int N)
{
    Console.Write(N * Math.Floor((
                      Math.Pow(10, N) - 1) / N));
}
 
// Driver code
public static void Main()
{
    int N = 2;
    smallestNumber(N);
}
}
 
// This code is contributed by Code_Mech

Javascript

<script>
 
// javascript program to find largest multiple
// of N containing N digits
 
 
// Function to find the largest 
// N digit multiple of N
 
function smallestNumber( N)
{
    document.write( N * Math.floor((Math.pow(10, N) - 1) / N));
}
 
// Driver code
let N = 2;
    smallestNumber(N);
 
// This code is contributed by todaysgaurav
 
</script>

Output:

Time Complexity: O(1)

Auxiliary Space: O(1)

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