day 25 complete -- 2023 complete

1 files changed, 43 insertions, 0 deletions

diff --git a/aoc2023-other/day-25/day-25.rkt b/aoc2023-other/day-25/day-25.rkt
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+#lang racket
+
+(require advent-of-code
+         threading
+         graph)
+
+(define input
+  (~> (fetch-aoc-input (find-session) 2023 25 #:cache #true)
+      (string-split "\n")
+      (map (curryr string-split ": ") _)))
+
+(define all-wires
+  (for*/list ([wire-diagram (in-list input)] [devices (in-list (string-split (second wire-diagram)))])
+    (list (car wire-diagram) devices)))
+
+;; instead of trying to solve the minimum cut problem, I generated the graph and
+;; rendered it in graphviz:
+
+; (define out (open-output-file "graphviz"))
+; (~> all-wires
+;     unweighted-graph/undirected
+;     graphviz
+;     (display out))
+; (close-output-port out)
+
+;; the bottleneck is very obvious on the graph --
+;; there's two large clusters of nodes, connected by just three edges
+;;
+;; from the graphviz output, the three critical wires are
+;; cpq-hlx
+;; hqp-spk
+;; chr-zlx
+
+(define remove-these-three '(("cpq" "hlx") ("hqp" "spk") ("chr" "zlx")))
+(define cut-wires
+  (for/list ([wire (in-list all-wires)] #:unless (member (sort wire string<?) remove-these-three))
+    wire))
+
+(~> cut-wires
+    unweighted-graph/undirected
+    scc
+    (map length _)
+    (apply * _))
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