Project Euler Problem 25

１０００桁を超える最初のfibonacci数は何個目か？

安直に。

target_len = 1000
fib = [1,1,2]
index = 3

while len(str(fib[2])) < target_len:
    index += 1
    fib = [fib[1], fib[2], fib[1] + fib[2]]

    if len(str(fib[2])) >= target_len:
        print index
        break

python prog.py 1.46s user 0.00s system 99% cpu 1.466 total