20161002, 11:13  #1 
"Robert Gerbicz"
Oct 2005
Hungary
2^{5}×7^{2} Posts 
October 2016

20161002, 14:43  #2  
"Rashid Naimi"
Oct 2015
Remote to Here/There
8C2_{16} Posts 
Quote:


20161002, 17:24  #3 
(loop (#_fork))
Feb 2006
Cambridge, England
3^{3}·239 Posts 
What a particularly uninteresting problem  ten lines of Pari code to munge through it in a few hours (and it can be a few minutes if you're willing to accept prior knowledge of the answer). It makes you wonder whether the setter was unaware of how big the libraries have grown now and expected people to write the calculatepi function too.
(I think you can get by with 1200 digit precision, which is really not that much, and it takes under 40 minutes) 
20161002, 17:58  #4 
"Serge"
Mar 2008
Phi(4,2^7658614+1)/2
11×19×47 Posts 
Boy, I feel even a bit glad that I forgot to look up this one...
For the first time in a few years, I think I could get to "metasolve" the category "solve 10 last problems" in Project Euler. I have one left, but it's tough! PE566... ________________________ EDIT: The answers for up to 8digits strings are L=2 38s with 35 L=3 301s with 459 L=4 818s with 1384 L=5 sikrit with XXXXX L=6 18032s with 029095 L=7 34090s with 1718077 L=8 324724s with 39668259 Last fiddled with by Batalov on 20161002 at 23:58 
20161002, 18:22  #5 
"Robert Gerbicz"
Oct 2005
Hungary
2^{5}×7^{2} Posts 

20161003, 00:11  #6 
"Serge"
Mar 2008
Phi(4,2^7658614+1)/2
11×19×47 Posts 
For L=9, the answer is 941873747 with a bit over 2megaseconds (557:22:48)
For L=10, the answer is 2087746140 using 5645117s Last fiddled with by Batalov on 20161003 at 01:17 Reason: ...yes ...L=10. 
20161003, 09:50  #7 
Romulan Interpreter
"name field"
Jun 2011
Thailand
2·17·293 Posts 
I agree with Tom and Serge, this problem is totally uninteresting. Even without arbitrary precision math, one could get the "strings" from anywhere on the web (wolfram, etc) and do simple string processing.

20161003, 09:53  #8 
"Robert Gerbicz"
Oct 2005
Hungary
2^{5}×7^{2} Posts 
For L=11: 17511073s with 38898554239, computed this in 16min using only PARIGp.

20161003, 14:56  #9 
"Serge"
Mar 2008
Phi(4,2^7658614+1)/2
11·19·47 Posts 
When I was 15, I wrote programs that computed pi, e, and M to a 100,000 digits (iirc), and my father ran them at the RFNC "supercomputer" (which was BESM6 and Elbrus), so this problem did get me to feel nostalgic for a split minute. The programs computed constants from scratch using school division and multiplication and were in Fortran and Algol68 if memory serves.

20161003, 17:42  #10 
"Robert Gerbicz"
Oct 2005
Hungary
1568_{10} Posts 
If you like to compute these constants then see (for example): http://www.spoj.com/problems/PIVAL/ . On spoj you can find the other two constants challenge problem. Note that these has strict code size limit=4096 bytes. And you can find also a challenge for golden ratio, but with different scoring system.
Returning to the original problem: For L=12: 173108889 sec;string=027143247568 For L=13: 396336569 sec;string=6766970531749 This time not used PariGp. For L=14 I've run out of memory. 
20161101, 13:35  #11 
Aug 2002
8451_{10} Posts 

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