USING: accessors combinators hash-sets hashtables kernel locals
math math.parser sequences sets vectors ;

IN: ant

: sum-digits ( n -- x )
    0 swap [ dup zero? ] [
        10 [ mod + ] [ /i ] 2bi
    ] until drop ;

TUPLE: point x y ;

C: <point> point

: walkable? ( point -- ? )
    [ x>> ] [ y>> ] bi [ sum-digits ] bi@ + 25 <= ;

:: ant ( -- total )
    HS{ } clone :> seen
    V{ } clone :> stack
    0 :> total!

    1000 1000 <point> stack push

    [ stack empty? total 10000 > or ] [
        stack pop :> p
        p seen in? [
            p seen adjoin
            p walkable? [
                total 1 + total!
                p clone [ 1 + ] change-x stack push
                p clone [ 1 - ] change-x stack push
                p clone [ 1 + ] change-y stack push
                p clone [ 1 - ] change-y stack push
            ] when
        ] unless
    ] until total ;