Smallest K digit number divisible by X

Integers X and K are given. The task is to find the smallest K-digit number divisible by X. 

Examples : 

Input : X = 83, K = 5
Output : 10043
10040 is the smallest 5 digit
number that is multiple of 83.

Input : X = 5, K = 2
Output : 10

A simple solution is to try all numbers starting from the smallest K digit number 
(which is 100…(K-1)times) and return the first number divisible by X.

An efficient solution would be :  

Compute MIN : smallest K-digit number (1000...(K-1)times)
If, MIN % X is 0, ans = MIN
else, ans = (MIN + X) - ((MIN + X) % X))
This is because there will be a number in 
range [MIN...MIN+X] divisible by X.

Output : 

10043

Time Complexity: O(logk)

Auxiliary Space: O(1)