Re: Re (tilly) 1: Finding sum of all digits from 1 to 1 million.

[PrakashK]

in reply to Re (tilly) 1: Finding sum of all digits from 1 to 1 million.
in thread Finding sum of all digits from 1 to 1 million.

a good exercise would be to write Perl code that efficiently calculates the sum of all of the digits in a range of integers.

Assuming sum(n) is the sum of all digits from 1 to n, sum_range(m, n) is the sum of all digits from m to n, and m < n, isn't the following true?

sum_range(m,n) = sum(n) - sum(m)

Or, did I totally get you wrong? /prakash

[tilly]

Off by one error again, your formula drops m from the answer. (And the obvious fix will need more cases if your range potentially includes negative integers.)

But still, you are essentially correct. After some wrapper logic, the problem really does boil down to being able to efficiently calculate the sum of the digits from 1 to n for any positive integer n.