Given two positive integers N and M. The task is to find M-th number whose sum of digits of a number until sum becomes single digit is N.
Input: N = 1, M = 3 Output: 19 The first two numbers being 1 and 9. Input: N = 2, M = 5 Output: 38 The first four numbers being 2, 11, 20 and 29.
A naive approach is to iterate for all numbers and keep a count of number whose sum returns N.
An efficient approach is to find the summation of digits till it becomes single digits in O(1) that has been discussed here. Hence the formula to find M-th number will be:
Mth number: (M-1)*9 + N
Below is the implementation of the above approach:
- Remove repeated digits in a given number
- Count ways to spell a number with repeated digits
- Recursive sum of digits of a number formed by repeated appends
- Find the Largest number with given number of digits and sum of digits
- Find smallest number with given number of digits and sum of digits
- Find the number of positive integers less than or equal to N that have an odd number of digits
- Find maximum number that can be formed using digits of a given number
- Find count of digits in a number that divide the number
- Find the smallest number whose digits multiply to a given number n
- Find the average of k digits from the beginning and l digits from the end of the given number
- Count of integers in a range which have even number of odd digits and odd number of even digits
- Given a number n, find the first k digits of n^n
- Find first and last digits of a number
- Find the number of integers from 1 to n which contains digits 0's and 1's only
- Find the n-th number made of even digits only
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