Left factorials: Difference between revisions
Added alternative C++ solution
(Alternative Rust solution) |
(Added alternative C++ solution) |
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!9000 has 31678 digits.
!10000 has 35656 digits.
</pre>
===Faster alternative===
{{libheader|GMP}}
<lang cpp>#include <iostream>
#include <gmpxx.h>
template <typename integer>
class left_factorial_generator {
public:
integer next() {
integer result = next_;
next_ += factorial_;
factorial_ *= n_++;
return result;
}
private:
unsigned int n_ = 1;
integer factorial_ = 1;
integer next_ = 0;
};
int main() {
left_factorial_generator<mpz_class> lf;
int i = 0;
std::cout << "Left factorials 0 through 10:\n";
for (; i <= 10; ++i)
std::cout << "!" << i << " = " << lf.next() << '\n';
std::cout << "Left factorials 20 through 110, by tens:\n";
for (; i <= 110; ++i) {
auto n = lf.next();
if (i % 10 == 0)
std::cout << "!" << i << " = " << n << '\n';
}
std::cout << "Lengths of left factorials 1000 through 10000, by thousands:\n";
for (; i <= 10000; ++i) {
auto n = lf.next();
if (i % 1000 == 0)
std::cout << "length of !" << i << " = " << n.get_str().size() << '\n';
}
return 0;
}</lang>
{{out}}
<pre>
Left factorials 0 through 10:
!0 = 0
!1 = 1
!2 = 2
!3 = 4
!4 = 10
!5 = 34
!6 = 154
!7 = 874
!8 = 5914
!9 = 46234
!10 = 409114
Left factorials 20 through 110, by tens:
!20 = 128425485935180314
!30 = 9157958657951075573395300940314
!40 = 20935051082417771847631371547939998232420940314
!50 = 620960027832821612639424806694551108812720525606160920420940314
!60 = 141074930726669571000530822087000522211656242116439949000980378746128920420940314
!70 = 173639511802987526699717162409282876065556519849603157850853034644815111221599509216528920420940314
!80 = 906089587987695346534516804650290637694024830011956365184327674619752094289696314882008531991840922336528920420940314
!90 = 16695570072624210767034167688394623360733515163575864136345910335924039962404869510225723072235842668787507993136908442336528920420940314
!100 = 942786239765826579160595268206839381354754349601050974345395410407078230249590414458830117442618180732911203520208889371641659121356556442336528920420940314
!110 = 145722981061585297004706728001906071948635199234860720988658042536179281328615541936083296163475394237524337422204397431927131629058103519228197429698252556442336528920420940314
Lengths of left factorials 1000 through 10000, by thousands:
length of !1000 = 2565
length of !2000 = 5733
length of !3000 = 9128
length of !4000 = 12670
length of !5000 = 16322
length of !6000 = 20062
length of !7000 = 23875
length of !8000 = 27749
length of !9000 = 31678
length of !10000 = 35656
</pre>
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