From 0755910e65ae32b70b0c40ff76e1106aceeeb1e0 Mon Sep 17 00:00:00 2001
From: Clyne Sullivan <clyne@bitgloo.com>
Date: Sat, 18 Dec 2021 17:25:38 -0500
Subject: [PATCH] add day 18

---
 day18/partboth.clj | 97 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 97 insertions(+)
 create mode 100644 day18/partboth.clj

diff --git a/day18/partboth.clj b/day18/partboth.clj
new file mode 100644
index 0000000..b3b97ca
--- /dev/null
+++ b/day18/partboth.clj
@@ -0,0 +1,97 @@
+(require '[clojure.core.reducers :as r])
+(require '[clojure.set :as set])
+(require '[clojure.zip :as z])
+
+(defn zip-depth [loc]
+  (loop [l loc d 0] (if (nil? l) d (recur (z/up l) (inc d)))))
+
+(defn zip-prev-num [loc]
+  (loop [l loc]
+    (if-let [prev (z/prev l)]
+      (if (not (z/branch? prev))
+        prev
+        (recur prev)))))
+
+(defn zip-next-num [loc]
+  (loop [l loc]
+    (if-let [nxt (z/next l)]
+      (if (not (z/branch? nxt))
+        (when (some? (z/node nxt)) nxt)
+        (recur nxt)))))
+
+(defn snailfish-explode [tree]
+  (loop [node (z/vector-zip tree)]
+    (if (z/end? node)
+      node
+      (if (and (z/branch? node)
+               (= 2 (count (z/children node)))
+               (and (not (z/branch? (z/down node))) (not (z/branch? (z/next (z/down node)))))
+               (> (zip-depth node) 5))
+        (let [children (z/children node)
+              nnode    (z/replace node 0)]
+          (if-let [prev (zip-prev-num nnode)]
+            (z/root
+              (let [new-prev (z/edit prev + (first children))]
+                (if-let [nxt (nth (iterate zip-next-num new-prev) 2)]
+                  (z/edit nxt + (second children))
+                  new-prev)))
+            (when-let [nxt (zip-next-num nnode)]
+              (z/root (z/edit nxt + (second children))))))
+        (recur (z/next node))))))
+
+(defn snailfish-split [tree]
+  (loop [node (z/vector-zip tree)]
+    (if (or (z/end? node) (nil? (z/node node)))
+      node
+      (if (and (not (z/branch? node)) (> (z/node node) 9))
+        (z/root
+          (z/replace node
+            (z/make-node node (z/node node)
+              (map long [(Math/floor (/ (z/node node) 2))
+                         (Math/ceil (/ (z/node node) 2))]))))
+        (recur (z/next node))))))
+
+(defn snailfish-magnitude [ntree]
+    (if (= 2 (count (z/children ntree)))
+      (let [cl (z/down ntree) cr (z/right cl)]
+        (+ (* 3 (if (z/branch? cl) (snailfish-magnitude cl) (z/node cl)))
+           (* 2 (if (z/branch? cr) (snailfish-magnitude cr) (z/node cr)))))
+      (loop [node (z/down ntree) sum 0]
+        (if (nil? node)
+          sum
+          (recur (z/right node)
+                 (+ sum (if (z/branch? node) (snailfish-magnitude node) (z/node node))))))))
+
+(defn snailfish-solve [add-list]
+  (snailfish-magnitude
+    (loop [result     (z/vector-zip (vec (take 2 add-list)))
+           next-input (drop 2 add-list)]
+      (let [explode (snailfish-explode result)]
+        (if (nil? (second explode))
+          (recur explode next-input)
+          (let [splt (snailfish-split result)]
+            (if (nil? (second splt))
+              (recur splt next-input)
+              (if (empty? next-input)
+                result
+                (recur (z/vector-zip
+                         [(vec (z/children result)) (first next-input)])
+                       (rest next-input))))))))))
+
+; Build input list
+(def input (->> (slurp "./in")
+                clojure.string/split-lines
+                (map read-string)))
+
+; Part 1
+(println (snailfish-solve input))
+
+; Part 2
+(->> (let [input-set (set input)]
+       (for [in input in2 (set/difference input-set (set [in]))]
+         [in in2]))
+     (into [])
+     (r/map snailfish-solve)
+     (r/fold (r/monoid max (constantly 0)))
+     (println))
+