c++ - Faculty and factors with recursion -


i'm trying implement recursion in different way, i'm stumped implementation of said math.

here's code:

#include <iostream> using namespace std;    template <const int n> class faculty { public:     static const int val = faculty<n - 1>::val * n; //recursion!!!! };   //for when 1!, return value of 1! template <> class faculty<1> { public:     static const int val = 1; };   //falling factorial template <const int n, const int k> class fallingcfactorial { public:     static const int n_k = faculty<n>::val / faculty<n - k>::val;     // (n * n - 1 * ... * 1) / ((n - k) * (n - k + 1) * ... * 1) };    // implementing factorial different way // (n * (n - 1) * ... * (n - k + 1))   //for when n = k output = 1 template <const int n> class fallingcfactorial<n, n> { public:     static const int n_k = 1;  };   int main(void) {     cout << "faculty of 5 (1*2*3*4*5): " << faculty<5>::val << endl;     cout << "n(10)_k(5) = " << fallingcfactorial<10, 5>::n_k << endl; }

trying (n * (n - 1) * ... * (n - k + 1)) way, fail @ implementing in code. math isn't absolute strong suit, ok.

the use of templates little bit tricky. think should solve problem:

#include <iostream> using namespace std;  template <const int n, const int k> class fallingfactorial { public:     static const int n_k = fallingfactorial<n - 1, k>::n_k * n; };  template <const int n> class fallingfactorial<n, n> { public:     static const int n_k = 1; };  int main(void) {     cout << fallingfactorial<10, 5>::n_k << endl;     return 0; }

this example based on partial template specialization (template <const int n> class fallingfactorial<n, n>). when template class called best matching , "most specialized" template used. older compilers doesn't support partial specialization (see wiki).


Comments

Post a Comment

Popular posts from this blog

html - Outlook 2010 Anchor (url/address/link) -

i'm trying link specific pdf page msoutlook'10 or msword'10, #page=... anchor particularly useful , works fine elsewhere. unfortunately when click [ctr-k] in outlook or winword, links re-formatted assuming unc path. pdf file located on shared drive. using "file:" prefix links open pdf in adobe reader (outside of browser), , "http:" open inside browser. issue seem need open in browser "file:" prefix in order anchor work. know anchors work inside browser. outlook uses windows/explorer default program (based on file extension) seems open in adobe reader neglecting anchor. is aware of solution, link specific page or bookmark of shared-pdf ms outlook and/or winword link? common references: mailermailer.com/...anchor-tags-html-emails campaignmonitor.com/...anchor-links-in-email-newsletters/ stackoverflow.com/...anchor-in-pdf-document
Read more

javascript - Why does running this loop 9 times take 100x longer than running it 8 times? -

consider code: test = function() { } t = new test(); (var = 0; < 8; i++) { result = t instanceof test; } if change number of iterations 8 9 , loop take 100 times longer complete in latest version of firefox (41.0.1). tested on 2 different pcs , magic limit 8. here jsperf test used: http://jsperf.com/instanceof-8-times-vs-9-times does have idea why might happen? seems specific instanceof . not happen if else object, example check property. note: filed bugzilla bug this. jan de mooij mozilla team has posted details in bugzilla thread . here's simplistic interpretation of highly technical answers: in i < 8 case, firefox smart enough hoist result = t instanceof test; statement out of loop (according tests, doesn't seem omit altogether). in i < 9 case, apparently doesn't optimization . why? reason not clear, related fact 9 iterations threshold above function considered "hot" enough run through jit compiler. i < 8 cas...
Read more

Getting gateway time-out Rails app with Nginx + Puma running on Digital Ocean -

following this guide setup app on digital ocean droplet, not working. site not loading , it's throwing: "gateway time-out". the puma server works, since ps aux | grep puma prints: root 15878 0.0 0.4 376832 2168 ? sl 12:50 0:00 puma 2.13.4 (unix:///var/www/myapp/shared/tmp/sockets/myapp-puma.sock) [20150930164940] root 15881 0.0 0.7 903676 3692 ? sl 12:50 0:06 puma: cluster worker 0: 15878 [20150930164940] root 24654 0.0 0.1 11748 916 pts/2 s+ 18:00 0:00 grep --color=auto puma my nginx config: user root; worker_processes 1; events { worker_connections 1024; } http { upstream puma { server unix:///var/www/myapp/shared/tmp/sockets/myapp-puma.sock; } server { listen 80; server_name myapp.com; root /var/www/myapp/current/public; access_log /var/www/myapp/current/log/access.log; error_log /...
Read more