Project Euler Problem 145
For some reason there are no solutions above 10**8, so you can reduce the search space by a lot. In addition, you never
need to check numbers divisble by 10, reducing it further. I think I've narrowed the valid search space to ~4.5% of the
one given by the problem.
Revision 1:
Turns out that using the built-in repr function makes this go much (~5x) faster, so I'll switch to that until I find a
narrower solution. It's very nearly at the 60s mark now.
Revision 2:
I reduced the search space by trial and error, getting it down to ~3.15% of the original
Problem:
Some positive integers n have the property that the sum [ n + reverse(n) ] consists entirely of odd (decimal) digits.
For instance, 36 + 63 = 99 and 409 + 904 = 1313. We will call such numbers reversible; so 36, 63, 409, and 904 are
reversible. Leading zeroes are not allowed in either n or reverse(n).
There are 120 reversible numbers below one-thousand.
How many reversible numbers are there below one-billion (10^9)?
1.8.11
