1 ! Copyright (c) 2008 Aaron Schaefer.
2 ! See https://factorcode.org/license.txt for BSD license.
3 USING: kernel math ranges project-euler.common sequences ;
6 ! https://projecteuler.net/index.php?section=problems&id=38
11 ! Take the number 192 and multiply it by each of 1, 2, and 3:
17 ! By concatenating each product we get the 1 to 9 pandigital, 192384576. We
18 ! will call 192384576 the concatenated product of 192 and (1,2,3)
20 ! The same can be achieved by starting with 9 and multiplying by 1, 2, 3, 4,
21 ! and 5, giving the pandigital, 918273645, which is the concatenated product of
24 ! What is the largest 1 to 9 pandigital 9-digit number that can be formed as
25 ! the concatenated product of an integer with (1,2, ... , n) where n > 1?
31 ! Only need to search 4-digit numbers starting with 9 since a 2-digit number
32 ! starting with 9 would produce 8 or 11 digits, and a 3-digit number starting
33 ! with 9 would produce 7 or 11 digits.
37 : (concat-product) ( accum n multiplier -- m )
41 [ * number>digits append! ] 2keep 1 + (concat-product)
44 : concat-product ( n -- m )
45 V{ } clone swap 1 (concat-product) ;
49 : euler038 ( -- answer )
50 9123 9876 [a..b] [ concat-product ] map [ pandigital? ] filter supremum ;
52 ! [ euler038 ] 100 ave-time
53 ! 11 ms ave run time - 1.5 SD (100 trials)