From 36173c1a15208a108e55e90ccc359dd2207c16e5 Mon Sep 17 00:00:00 2001
From: Joshua Seigler <joshua@seigler.net>
Date: Sat, 18 Dec 2021 03:54:44 -0500
Subject: [PATCH] day 18

---
 .aocrunner.json     |  12 ++---
 README.md           |  12 ++---
 src/day18/README.md |   9 ++++
 src/day18/index.js  | 104 ++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 125 insertions(+), 12 deletions(-)
 create mode 100644 src/day18/README.md
 create mode 100644 src/day18/index.js

diff --git a/.aocrunner.json b/.aocrunner.json
index 6f31817..ef07057 100644
--- a/.aocrunner.json
+++ b/.aocrunner.json
@@ -257,16 +257,16 @@
     },
     {
       "part1": {
-        "solved": false,
-        "result": null,
+        "solved": true,
+        "result": "4235",
         "attempts": [],
-        "time": null
+        "time": 35.41
       },
       "part2": {
-        "solved": false,
-        "result": null,
+        "solved": true,
+        "result": "4659",
         "attempts": [],
-        "time": null
+        "time": 268.36
       }
     },
     {
diff --git a/README.md b/README.md
index ba5b07e..4392cd4 100644
--- a/README.md
+++ b/README.md
@@ -28,7 +28,7 @@
 [![Day](https://badgen.net/badge/15/%E2%98%85%E2%98%85/green)](src/day15)
 [![Day](https://badgen.net/badge/16/%E2%98%85%E2%98%85/green)](src/day16)
 [![Day](https://badgen.net/badge/17/%E2%98%85%E2%98%85/green)](src/day17)
-![Day](https://badgen.net/badge/18/%E2%98%86%E2%98%86/gray)
+[![Day](https://badgen.net/badge/18/%E2%98%85%E2%98%85/green)](src/day18)
 ![Day](https://badgen.net/badge/19/%E2%98%86%E2%98%86/gray)
 ![Day](https://badgen.net/badge/20/%E2%98%86%E2%98%86/gray)
 ![Day](https://badgen.net/badge/21/%E2%98%86%E2%98%86/gray)
@@ -188,9 +188,9 @@ Both parts: 430.38ms
 
 ```
 Day 18
-Time part 1: -
-Time part 2: -
-Both parts: -
+Time part 1: 38.77ms
+Time part 2: 147.3ms
+Both parts: 186.07000000000002ms
 ```
 
 ```
@@ -243,8 +243,8 @@ Both parts: -
 ```
 
 ```
-Total stars: 34/50
-Total time: 2333.3799999999997ms
+Total stars: 36/50
+Total time: 2519.45ms
 ```
 
 <!--/RESULTS-->
diff --git a/src/day18/README.md b/src/day18/README.md
new file mode 100644
index 0000000..a2db159
--- /dev/null
+++ b/src/day18/README.md
@@ -0,0 +1,9 @@
+# 🎄 Advent of Code 2021 - day 18 🎄
+
+## Info
+
+Task description: [link](https://adventofcode.com/2021/day/18)
+
+## Notes
+
+...
\ No newline at end of file
diff --git a/src/day18/index.js b/src/day18/index.js
new file mode 100644
index 0000000..1b49070
--- /dev/null
+++ b/src/day18/index.js
@@ -0,0 +1,104 @@
+import run from "aocrunner"
+
+const parseInput = (rawInput) => rawInput.trim().split`\n`.map(JSON.parse)
+
+/**
+ * @returns [exploded, toAddLeft, newValue, toAddRight]
+ */
+function explode(p, maxDepth = 4) {
+  if (typeof p === "number") return [false, undefined, p, undefined]
+  const [left, right] = p
+  if (maxDepth == 0) return [true, left, 0, right]
+  let [exploded, toAddLeft, newValue, toAddRight] = explode(left, maxDepth - 1)
+  if (exploded) {
+    return [true, toAddLeft, [newValue, addRight(right, toAddRight)], undefined]
+  }
+  ;[exploded, toAddLeft, newValue, toAddRight] = explode(right, maxDepth - 1)
+  if (exploded) {
+    return [true, undefined, [addLeft(left, toAddLeft), newValue], toAddRight]
+  }
+  return [false, undefined, p, undefined]
+}
+
+function addRight(v, n) {
+  // to the right means expanding the left side
+  if (n === undefined) return v
+  if (typeof v === "number") return v + n
+  return [addRight(v[0], n), v[1]]
+}
+
+function addLeft(v, n) {
+  // to the left means expanding the right side
+  if (n === undefined) return v
+  if (typeof v === "number") return v + n
+  return [v[0], addLeft(v[1], n)]
+}
+
+/** @returns [changed, newValue] */
+function split(v) {
+  if (typeof v === "number") {
+    if (v > 9) return [true, [Math.floor(v / 2), Math.ceil(v / 2)]]
+    return [false, v]
+  }
+  let [left, right] = v
+  let [changed, newValue] = split(left)
+  if (changed) {
+    return [true, [newValue, right]]
+  }
+  ;[changed, newValue] = split(right)
+  if (changed) {
+    return [true, [left, newValue]]
+  }
+  return [false, v]
+}
+
+function add(a, b) {
+  let changed,
+    p = [a, b]
+  while (true) {
+    ;[changed, , p] = explode(p)
+    if (changed) continue
+    ;[changed, p] = split(p)
+    if (changed) continue
+    break
+  }
+  return p
+}
+
+function magnitude(v) {
+  return typeof v === "number" ? v : 3 * magnitude(v[0]) + 2 * magnitude(v[1])
+}
+
+const part1 = (rawInput) => {
+  const input = parseInput(rawInput)
+  return magnitude(input.reduce(add))
+}
+
+const part2 = (rawInput) => {
+  const input = parseInput(rawInput)
+  let best = -Infinity
+  for (let i = 0; i < input.length; i++)
+    for (let j = i + 1; j < input.length; j++)
+      best = Math.max(
+        best,
+        magnitude(add(input[i], input[j])),
+        magnitude(add(input[j], input[i])),
+      )
+  return best
+}
+
+run({
+  part1: {
+    tests: [
+      // { input: ``, expected: "" },
+    ],
+    solution: part1,
+  },
+  part2: {
+    tests: [
+      // { input: ``, expected: "" },
+    ],
+    solution: part2,
+  },
+  trimTestInputs: true,
+})