From a496300ed475c87de6a17a79ff6ba6f0ee607ab8 Mon Sep 17 00:00:00 2001
From: Nikita Hasert <nikitahasert@gmail.com>
Date: Sat, 16 Dec 2023 12:34:43 +0100
Subject: [PATCH] Day 16: Solve part 1 and 2

---
 src/advent_of_code_2023/day15.clj       | 64 +++++++++++++++++++++++--
 test/advent_of_code_2023/day15_test.clj | 21 ++++----
 2 files changed, 73 insertions(+), 12 deletions(-)

diff --git a/src/advent_of_code_2023/day15.clj b/src/advent_of_code_2023/day15.clj
index 7c6da76..243e3d4 100644
--- a/src/advent_of_code_2023/day15.clj
+++ b/src/advent_of_code_2023/day15.clj
@@ -2,8 +2,66 @@
   (:require
    [advent-of-code-2023.utils.string :as u]))
 
-(defn parse-input [input])
+(defn parse-input [input]
+  (mapv (fn [ascii]
+          (let [op (re-find #"=|-" ascii)
+                [label focal-length] (u/split-sections ascii #"=|-")]
+            (if (= op "=")
+              [ascii label :assign (Long/parseLong focal-length)]
+              [ascii label :remove])))
+        (u/split-sections input #",")))
 
-(defn day15-1 [parsed-input])
+(defonce ^:private ascii-hash
+  (memoize (fn [ascii]
+             (reduce (fn [^long cv ^long a] (-> cv (+ a) (* 17) (rem 256)))
+                     0 (mapv long ascii)))))
 
-(defn day15-2 [parsed-input])
\ No newline at end of file
+(defn day15-1 [lenses]
+  (transduce
+   (comp
+    (map first)
+    (map ascii-hash))
+   + lenses))
+
+(defn- add-lens [{:keys [positions] :as b} label focal-length]
+  (let [ah (ascii-hash label)
+        relevant-box (positions ah)
+        pos (or (get relevant-box label) (count relevant-box))]
+    (-> b
+        (assoc-in ,,, [:focal-lengths label] focal-length)
+        (assoc-in ,,, [:positions ah label] pos))))
+
+(defn- remove-lens [{:keys [positions] :as b} label]
+  (let [ah (ascii-hash label)
+        relevant-box (positions ah)]
+    (if-let [pos (get relevant-box label)]
+      (transduce
+       (comp
+        (filter (fn [[_ ^long p]] (< ^long pos p)))
+        (map first))
+       (fn
+         ([box] box)
+         ([box lbl]
+          (update-in box [:positions ah lbl] dec)))
+       (update-in b [:positions ah] dissoc label) relevant-box)
+      b)))
+
+(defn- focus-power [{:keys [focal-lengths positions]}]
+  (transduce
+   (comp
+    (mapcat (fn [[^long box-nr order]]
+              (mapv (fn [[lbl ^long pos]] (* (inc box-nr)
+                                             (inc pos)
+                                             ^long (focal-lengths lbl)))
+                    order))))
+   + positions))
+
+(defn day15-2 [lenses]
+  (focus-power
+   (reduce (fn [boxes [_ label op focal-length]]
+             (if (= op :assign)
+               (add-lens boxes label focal-length)
+               (remove-lens boxes label)))
+           {:focal-lengths {}
+            :positions {}}
+           lenses)))
\ No newline at end of file
diff --git a/test/advent_of_code_2023/day15_test.clj b/test/advent_of_code_2023/day15_test.clj
index fe50fcb..4f07779 100644
--- a/test/advent_of_code_2023/day15_test.clj
+++ b/test/advent_of_code_2023/day15_test.clj
@@ -4,26 +4,29 @@
    [advent-of-code-2023.day15 :refer :all]
    [advent-of-code-2023.test-utils :as tu]))
 
-(defonce ^:private example-input (parse-input ""))
+(defonce ^:private example-ascii "HASH")
+
+(defonce ^:private example-input 
+  (parse-input "rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7"))
 
 (def ^:private input (parse-input (tu/slurp-input "resources/day15.txt")))
 
+(deftest day15-1-example-ascii-test
+  (testing "day15-1 example ascii"
+    (is (= 52 (day15-1 [[example-ascii nil]])))))
+
 (deftest day15-1-example-test
   (testing "day15-1 example"
-    (is (= nil
-           (day15-1 example-input)))))
+    (is (= 1320 (day15-1 example-input)))))
 
 (deftest day15-1-test
   (testing "day15-1"
-    (is (= nil
-           (day15-1 input)))))
+    (is (= 504449 (day15-1 input)))))
 
 (deftest day15-2-example-test
   (testing "day15-2 example"
-    (is (= nil
-           (day15-2 example-input)))))
+    (is (= 145 (day15-2 example-input)))))
 
 (deftest day15-2-test
   (testing "day15-2"
-    (is (= nil
-           (day15-2 input)))))
+    (is (= 262044 (day15-2 input)))))