Given a digital root ‘D’ and number of digits ‘K’. The task is to print a number containing K digits that has its digital root equal to D. Print ‘-1’ if such a number does not exist.
Input: D = 4, K = 4 Output: 4000 No. of digits is 4. Sum of digits is also 4. Input: D = 0, K = 1 Output: 0
Approach: A key observation to solving this problem is that appending any number of 0s to a number does not change its digital root. Hence D followed by (K-1) 0’s is a simple solution.
Special case when D is 0 and K is not 1 does not have a solution since the only number with digital root 0 is 0 itself.
Below is the implementation of the above approach:
Time complexity: O(K)
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