Python Program for Largest K digit number divisible by X

Integers X and K are given. The task is to find highest K-digit number divisible by X. Examples:

Input : X = 30, K = 3
Output : 990
990 is the largest three digit 
number divisible by 30.

Input : X = 7, K = 2
Output : 98

An efficient solution is to use below formula.

ans = MAX - (MAX % X)
where MAX is the largest K digit 
number which is  999...K-times

The formula works on simple school method division. We remove remainder to get the largest divisible number. 

Python3

# Python code to find highest
# K-digit number divisible by X

def answer(X, K):

    # Computing MAX
    MAX = pow(10, K) - 1

    #returning ans
    return (MAX - (MAX % X))

X = 30;
K = 3;

print(answer(X, K));

# Code contributes by Mohit Gupta_OMG <(0_o)>

Output :

990

Time Complexity: O(logn)
Auxiliary Space: O(1)

Please refer complete article on Largest K digit number divisible by X for more details!