The task is to find the smallest number with given sum of digits as S and number of digits as D.

Example 1:
Input:
S = 9
D = 2
Output:
18
Explanation:
18 is the smallest number
possible with sum = 9
and total digits = 2.

Example 2:
Input:
S = 20
D = 3
Output:
299
Explanation:
299 is the smallest number
possible with sum = 20
and total digits = 3.

Your Task:
You don't need to read input or print anything. Your task is to complete the function smallestNumber() which takes the two integers S and D and returns a string which is the smallest number if possible, else return "-1".

Expected Time Complexity: O(D)
Expected Auxiliary Space: O(1)

Constraints:
1 ≤ S ≤ 100
1 ≤ D ≤ 6

见题面

见题面