1 USING: accessors kernel locals math ;
4 TUPLE: block two three ;
5 TUPLE: end { ways integer } ;
9 : <failure> 0 <end> ; inline
10 : <success> 1 <end> ; inline
12 : failure? ( t -- ? ) ways>> 0 = ; inline
14 : choice ( t p q -- t t ) [ [ two>> ] [ three>> ] bi ] 2dip bi* ; inline
16 GENERIC: merge ( t t -- t )
17 GENERIC# block-merge 1 ( t t -- t )
18 GENERIC# end-merge 1 ( t t -- t )
19 M: block merge block-merge ;
20 M: end merge end-merge ;
21 M: block block-merge [ [ two>> ] bi@ merge ]
22 [ [ three>> ] bi@ merge ] 2bi <block> ;
23 M: end block-merge nip ;
24 M: block end-merge drop ;
25 M: end end-merge [ ways>> ] bi@ + <end> ;
27 GENERIC: h-1 ( t -- t )
28 GENERIC: h0 ( t -- t )
29 GENERIC: h1 ( t -- t )
30 GENERIC: h2 ( t -- t )
32 M: block h-1 [ h1 ] [ h2 ] choice merge ;
33 M: block h0 drop <failure> ;
34 M: block h1 [ [ h1 ] [ h2 ] choice merge ]
35 [ [ h0 ] [ h1 ] choice merge ] bi <block> ;
36 M: block h2 [ h1 ] [ h2 ] choice merge <failure> swap <block> ;
38 M: end h-1 drop <failure> ;
40 M: end h1 drop <failure> ;
41 M: end h2 dup failure? [ <failure> <block> ] unless ;
43 : next-row ( t -- t ) [ h-1 ] [ h1 ] choice swap <block> ;
45 : first-row ( n -- t )
46 [ <failure> <success> <failure> ] dip
47 1- [| a b c | b c <block> a b ] times 2drop ;
49 GENERIC: total ( t -- n )
50 M: block total [ total ] dup choice + ;
53 : solve ( width height -- ways )
54 [ first-row ] dip 1- [ next-row ] times total ;
56 : euler215 ( -- ways ) 32 10 solve ;