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;What is the first term in the
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;Fibonacci sequence to contain 1000 digits?
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(define (square x) (* x x))
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(define (pow man exp)
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(cond
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((= exp 0) 1)
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((< exp 0) (/ 1 (pow exp (- man))))
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((even? exp) (square (pow man (/ exp 2))))
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((odd? exp) (* man (square (pow man (/ (- exp 1) 2)))))
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(else #f)))
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(define (prob25 digits)
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(let ((big-const (pow 10 (- digits 1))))
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(let fib ((first 1) (second 1) (count 1))
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(if (>= first big-const)
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count
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(begin
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;(display first) (display " ") (display count) (newline)
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(fib second (+ first second) (+ count 1))
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)))
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)
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)
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-
(prob25 1000)
Archive for November, 2008
Euler problem 25
Friday, November 21st, 2008Coding C
Thursday, November 13th, 2008I’ve been taking a break from my other projects to learn C. Since I already know C++ fairly well, this is most fun when I write hideous C involving pointer arithmetic. Right now I’m writing an interpreter (or more accurately I’m starting by writing a tokenizer, which isn’t working yet and which I may not choose to go past.
More importantly, I’m doing the whole thing over ssh on a BSD box, thus learning *nix at the same time. Since I used about three commands, I’m not learning *much* but there you go.
Euler Problem 1
Monday, November 3rd, 2008I’ve decided to do a series of posts with my solutions to the Euler problems. They’ll be tagged with “euler”, and once I figure out how I’ll stop them from showing up on the main page.
This is the first Euler Problem
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(define sum
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(lambda (x) (apply + x)))
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(define product
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(lambda x (apply * x)))
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(define sum-1-to-n
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(lambda (x) (* (/ 1 2) x (+ x 1))))
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(define (1+ x) (+ x 1))
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(define (-1+ x) (- x 1))
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(let
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((smalllist '(3 5 6 9 10 12 15))
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(num15s (quotient 1000 15)))
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"(* num15s 15) -> 990, so we add the last few by hand"
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(+ (* 15
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(length smalllist)
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(sum-1-to-n (-1+ num15s)))
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(* num15s (sum smalllist))
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993 995 996 999))
Continuing project, programming contest, perl
Sunday, November 2nd, 2008The project I’m working on I briefly mentioned last post is a deliberately simple roguelike set in a branching dungeon. It’s 60-70% done at current, and I’ll say no more until I at least get to final bugfixing.
I went to the ACM programming contest, in which our school placed very average. I had more fun that I expected from the day before and less than from the week before. I had lots of delicious free food. I’d do it again, overall, and be more interested in doing so if I knew my team well ahead of time.
I started learning perl, which looks exactly as disgusting as everyone says it is. It seems useful. It has very odd array/hash behavior which relate to its origin in string processing. An array of three arrays is just the contents of each of those three. To make the kind of thing I want, you need to make explicit reference variables. Interestingly, the fact that you can only pass one array (because they’re flattened) to a function means that everything is passed by value to functions. To my knowledge this is also true of the assignment operator. Since perl as I mentioned supports references, this is to my liking… the array flattening less so.
Regular expressions are as always kickass, and I understand perl’s engine is the best to be found. I really need to get a Linux system soon so I can do fun things like use the “grep” command or have very large text consoles.