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comp.lang.lisp

Project Euler 26.

William James

3/18/2016 7:15:00 AM

Find the value of d < 1000 for which 1/d contains the longest
recurring cycle in its decimal fraction part.


OCaml:

#load "nums.cma";;
open Num;;
#load "str.cma";;

let rec reduce s =
if Str.string_match (Str.regexp "\\(.+\\)\\1+$") s 0
then reduce (Str.matched_group 1 s)
else s ;;

let examine d =
let s = approx_num_fix 4_000 (Int 1 // Int d) in
if
Str.string_match (Str.regexp ".*\\(......+\\)\\1\\1") s 0
then
let cycled = reduce (Str.matched_group 1 s) in
(String.length cycled, d, cycled)
else (0,0,"") ;;

let best = ref (0,0,"") ;;
for d = 3 to 999 do
best := max !best (examine d)
done ;;
let (len,n,_) = !best in
Printf.printf "%d yields longest cycle (length %d)\n" n len;;

983 yields longest cycle (length 982)


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