Project Euler Problem 25

問題

The Fibonacci sequence is defined by the recurrence relation:

    F_(n) = F_(n−1) + F_(n−2), where F_(1) = 1 and F_(2) = 1.

Hence the first 12 terms will be:

    F_(1) = 1
    F_(2) = 1
    F_(3) = 2
    F_(4) = 3
    F_(5) = 5
    F_(6) = 8
    F_(7) = 13
    F_(8) = 21
    F_(9) = 34
    F_(10) = 55
    F_(11) = 89
    F_(12) = 144

The 12th term, F_(12), is the first term to contain three digits.

What is the first term in the Fibonacci sequence to contain 1000 digits?

ソース

a = 1
b = 1
i = 1
while a.to_s.size != 1000 do
	a, b = b, a + b
	i += 1
end
puts i

解答

4782

感想

Rubyだから出来る芸当！