1000-digit Fibonacci number
AUTHOR
Flavio Poletti
https://projecteuler.net/problem=25
The Fibonacci sequence is defined by the recurrence relation:
Fn = Fn1 + Fn2, where F1 = 1 and F2 = 1. Hence the first 12 terms will be:
F1 = 1
F2 = 1
F3 = 2
F4 = 3
F5 = 5
F6 = 8
F7 = 13
F8 = 21
F9 = 34
F10 = 55
F11 = 89
F12 = 144
The 12th term, F12, is the first term to contain three digits.
What is the first term in the Fibonacci sequence to contain 1000 digits?
use v6;
sub MAIN(Int :$length = 1000, Bool :$boring = False) {
if $boring {
my ($x, $y, $c) = (1, 1, 2);
($x, $y, $c) = ($y, $x + $y, $c + 1) while $y.chars < $length;
$c.say;
return;
}
my @fibs = 0, 1, *+* ... *;
((1..*).grep:{@fibs[$_].chars == $length})[0].say;
return;
}
# vim: expandtab shiftwidth=4 ft=perl6