2023 day 8

2023/day08-haunted-wasteland/day08.jl

@@ -0,0 +1,40 @@
+fh = open("input")
+
+# Read turns
+tstring = collect(readline(fh))
+turns = map(tstring) do x
+    x == 'L' && return 1
+    x == 'R' && return 2
+end
+readline(fh)
+
+# Read nodes
+nodes = Dict{AbstractString,Tuple{AbstractString,AbstractString}}()
+while !eof(fh)
+    line = readline(fh)
+    node = line[1:3]
+    nodeleft = line[8:10]
+    noderght = line[13:15]
+    nodes[node] = (nodeleft,noderght)
+end
+
+function pathlength(pred, start, nodes, turns)
+    let node = start, n = 0, pos=1
+        while !pred(node)
+            node = nodes[node][turns[pos]]
+            n += 1
+            pos += 1
+            if pos > length(turns)
+                pos = 1
+            end
+        end
+        return n
+    end
+end
+
+println("Part 1: ", pathlength(x->x=="ZZZ", "AAA", nodes, turns))
+
+let ghosts = filter(x->x[end]=='A', collect(keys(nodes)))
+    paths = map(g->pathlength(x->x[end]=='Z', g, nodes, turns), ghosts)
+    println("Part 2: ", lcm(paths...))
+end