Day 8

Author

Julia Romanowska

The input

First line are the directions. Afterwards, there are “nodes”.

root = dirname(@__FILE__);
input_file = joinpath(root, "..", "..", "DATA", "2023", "input_day08.txt");
#input_file = joinpath(root, "..", "..", "DATA", "2023", "example_input_day08.txt");
input_data = read(open(input_file, "r"), String);

directions , nodes_raw = split(input_data, "\n\n");
nodes = CSV.read(
    IOBuffer(nodes_raw),
    DataFrame;
    header = ["name", "value"],
    delim = " = "
)

702×2 DataFrame

677 rows omitted

Row	name	value
	String3	String15
1	NFK	(LMH, RSS)
2	SLJ	(NBT, CDG)
3	SKX	(SRC, KKX)
4	LRB	(MNG, FSH)
5	QMQ	(DMG, QRV)
6	VRB	(PGG, PRG)
7	QNB	(PFD, FFQ)
8	BPK	(GFF, DFF)
9	JTD	(NVV, VLD)
10	PXD	(VNV, BDS)
11	PXP	(VFH, DLR)
12	XRH	(QMM, LDH)
13	GLV	(SDM, MFS)
⋮	⋮	⋮
691	VVS	(DJF, VFF)
692	QHG	(BQK, JHJ)
693	SLT	(PMX, HSS)
694	PDN	(KLX, DXM)
695	DLT	(XHV, PMS)
696	KKN	(FTF, FCX)
697	BLX	(QHG, LHJ)
698	GQH	(VDG, PQN)
699	VLD	(FGX, HVF)
700	KKX	(GQT, QXD)
701	KKJ	(BGQ, LFM)
702	LNJ	(FNL, HMG)

Part 1

The problem

I can create a dictionary of pairs.

function create_pairs(s::AbstractString)
    m = match(r"\((?<left>\w+), (?<right>\w+)\)", s);
    return (m["left"], m["right"])
end

create_pairs (generic function with 1 method)

transform!(
    nodes,
    :value => ByRow(create_pairs) => :value
)
nodes_dict = Dict(zip(nodes.name, nodes.value))

Dict{String3, Tuple{SubString{String}, SubString{String}}} with 702 entries:
  "LFQ" => ("LSB", "RLM")
  "DRR" => ("NFK", "TKJ")
  "FHF" => ("VCB", "BKJ")
  "GQT" => ("NRN", "GLV")
  "TKL" => ("KCR", "XCT")
  "HTL" => ("CBJ", "BFM")
  "CGB" => ("RLV", "DPR")
  "VGB" => ("MRC", "XPH")
  "GNL" => ("HNK", "QQJ")
  "XQQ" => ("QNL", "XXJ")
  "RHM" => ("TFS", "TQL")
  "CHQ" => ("JDC", "MRB")
  "PTK" => ("CMJ", "KDK")
  "FCX" => ("RLJ", "TQN")
  "PMB" => ("PJX", "LTG")
  "LRK" => ("CKB", "HXV")
  "KNP" => ("FFB", "SSB")
  "KSV" => ("HGD", "SBH")
  "VFF" => ("CLD", "NGD")
  "VRR" => ("TGC", "MTP")
  "LRD" => ("XHC", "PBG")
  "PKR" => ("RSQ", "SBS")
  "SKX" => ("SRC", "KKX")
  "CTR" => ("XBB", "VRB")
  "GGJ" => ("GXB", "MPF")
  ⋮     => ⋮

And then, I need the sequence of directions.

The solution

How many steps from “AAA” to “ZZZ”?

function check_directions(c::Char)
    if c == 'L'
        return 1
    end
    return 2
end

check_directions (generic function with 1 method)

start_node = "AAA";
end_node = "ZZZ";
steps = 0;
direction_no = 1;

cur_node = start_node;
while cur_node != end_node
    cur_direction = check_directions(directions[direction_no]);
    global cur_node = nodes_dict[cur_node][cur_direction];
    global steps += 1;
    global direction_no += 1;
    if direction_no == lastindex(directions) + 1
        global direction_no = 1;
    end
end

The trip takes: 19783 steps.