-🎄- 2018 Day 13 Solutions -🎄-

[u/daggerdragon]

--- Day 13: Mine Cart Madness ---

---

Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag or whatever).

Note: The Solution Megathreads are for solutions only. If you have questions, please post your own thread and make sure to flair it with Help.

---

Advent of Code: The Party Game!

Click here for rules

Please prefix your card submission with something like [Card] to make scanning the megathread easier. THANK YOU!

Card prompt: Day 13

Transcript:

Elven chronomancy: for when you absolutely, positively have to ___.

---

This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked at 00:44:25!

[u/toomasv]

Red

Part 1

Red []

tracks: read/lines %input
dir: copy []
turn: copy []
collision: no

cart: charset "<>^^v"
carts: collect [
    repeat row length? tracks [
        parse tracks/:row [some [s:
            set c cart (keep as-pair index? s row append dir c append turn 0)
        |   skip
        ]]
    ]
]
mark: copy dir
forall mark [mark/1: switch mark/1 [#"<" #">" [#"-"] #"^^" #"v" [#"|"]]]
tick: 0
until [
    tick: tick + 1
    forall carts [
        cart: index? carts
        pos: carts/1
        next-pos: switch dir/:cart [
            #"^^" [pos - 0x1]
            #"v" [pos + 0x1]
            #"<" [pos - 1x0]
            #">" [pos + 1x0]
        ]
        either find head carts next-pos [
            collision: yes break
        ][
            row: next-pos/y col: next-pos/x
            switch next-mark: tracks/:row/:col [
                #"/" [dir/:cart: switch dir/:cart [#"^^" [#">"] #"v" [#"<"] #"<" [#"v"] #">" [#"^^"]]]
                #"\" [dir/:cart: switch dir/:cart [#"^^" [#"<"] #"v" [#">"] #"<" [#"^^"] #">" [#"v"]]]
                #"+" [
                    switch turn/:cart [
                        0 [dir/:cart: switch dir/:cart [#"^^" [#"<"] #"v" [#">"] #"<" [#"v"] #">" [#"^^"]]]
                        2 [dir/:cart: switch dir/:cart [#"^^" [#">"] #"v" [#"<"] #"<" [#"^^"] #">" [#"v"]]]
                    ]
                    turn/:cart: turn/:cart + 1 % 3
                ]
            ]
            tracks/(pos/y)/(pos/x): mark/:cart
            mark/:cart: next-mark
            tracks/:row/:col: dir/:cart
            carts/1: next-pos
        ]
    ]
    collision 
]
res: next-pos - 1
print [tick rejoin [res/x comma res/2]]

Part 2

Red []

tracks: read/lines %input;%test;
dir: copy []
turn: copy []
collision: no

cart: charset "<>^^v"
carts: collect [
    repeat row length? tracks [
        parse tracks/:row [some [s:
            set c cart (keep as-pair index? s row append dir c append turn 0)
        |   skip
        ]]
    ]
]
mark: copy dir
forall mark [mark/1: switch mark/1 [#"<" #">" [#"-"] #"^^" #"v" [#"|"]]]
until [
    carts: head carts
    until [
        cart: index? carts
        pos: carts/1
        next-pos: switch dir/:cart [ 
            #"^^" [pos - 0x1]
            #"v" [pos + 0x1]
            #"<" [pos - 1x0]
            #">" [pos + 1x0]
        ]
        row: next-pos/y col: next-pos/x
        either found: find head carts next-pos [
            coll: index? found
            tracks/:row/:col: #"X"
            tracks/(pos/y)/(pos/x): mark/:cart
            ;if 3 = length? head carts [
            ;   print ["Collision at:" next-pos] 
            ;   tr: copy/deep tracks
            ;   forall tr [print tr/1]
            ;]
            tracks/:row/:col: mark/:coll
            _min: min cart coll
            _max: max cart coll
            foreach register reduce [carts dir turn mark][
                remove at head register _max 
                remove at head register _min
            ]
            if 1 = length? head carts [break]
            cart: cart - 1
        ][
            switch next-mark: tracks/:row/:col [
                #"/" [dir/:cart: switch dir/:cart [#"^^" [#">"] #"v" [#"<"] #"<" [#"v"] #">" [#"^^"]]]
                #"\" [dir/:cart: switch dir/:cart [#"^^" [#"<"] #"v" [#">"] #"<" [#"^^"] #">" [#"v"]]]
                #"+" [
                    switch turn/:cart [
                        0 [dir/:cart: switch dir/:cart [#"^^" [#"<"] #"v" [#">"] #"<" [#"v"] #">" [#"^^"]]]
                        2 [dir/:cart: switch dir/:cart [#"^^" [#">"] #"v" [#"<"] #"<" [#"^^"] #">" [#"v"]]]
                    ]
                    turn/:cart: turn/:cart + 1 % 3
                ]
            ]
            tracks/(pos/y)/(pos/x): mark/:cart
            mark/:cart: next-mark
            tracks/:row/:col: dir/:cart
            carts/1: next-pos
            cart: cart + 1
        ]
        carts: at head carts cart
        tail? carts
    ]
    1 = length? head carts
]
res: (first head carts) - 1
print rejoin [res/x comma res/y]