Given a number N, you need to find a divisor of N such that the Digital Root of that divisor is the greatest among all other divisors of N. If more than one divisors give the same greatest Digital Root then output the maximum divisor.
The Digital Root of a non-negative number can be obtained by repeatedly summing the digits of the number until we reach to a single digit. Example: DigitalRoot(98)=9+8=>17=>1+7=>8(single digit!). The task is to print the greatest divisor having the greatest Digital Root followed by a space and the Digital Root of that divisor.
Input: N = 10
Output: 5 5
The divisors of 10 are: 1, 2, 5, 10. The Digital Roots of these divisors are as follows:
1=>1, 2=>2, 5=>5, 10=>1. The greatest Digital Root is 5 which is produced by divisor 5, so answer is 5 5
Input: N = 18
Output: 18 9
The divisors of 18 are: 1, 2, 3, 6, 9, 18. The Digital Roots of these divisors are as follows:
1=>1, 2=>2, 3=>3, 6=>6, 9=>9, 18=>9. As we can see that 9 and 18 both have the greatest Digital Root of 9. So we select the maximum of those divisors, that is Max(9, 18)=18. So answer is 18 9
A naive approach will be to iterate till N and find all the factors and their digit sums. Store the largest among them and print them.
Time Complexity: O(N)
An efficient approach is to loop till sqrt(N), then the factors will be i and n/i. Check for the largest digit sum among them, in case of similar digit sums, store the larger factor. Once the iteration is completed, print them.
Below is the implementation of the above approach.
Time Complexity: O(sqrt(N))
- Digital Root (repeated digital sum) of the given large integer
- Numbers in a Range with given Digital Root
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- Greatest Integer Function
- Sum of greatest odd divisor of numbers in given range
- Greatest number less than equal to B that can be formed from the digits of A
- Greatest divisor which divides all natural number in range [L, R]
- N-th root of a number
- Square root of a number using log
- Square root of an integer
- Fast inverse square root
- Find cubic root of a number
- Program to calculate Root Mean Square
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