From cd1ab561707e01fc8d60f88fae6853b77cdb8f39 Mon Sep 17 00:00:00 2001
From: Sven Weidauer <sven@5sw.de>
Date: Tue, 14 Dec 2021 22:33:06 +0100
Subject: [PATCH] Day 14

---
 day14.swift | 151 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 151 insertions(+)
 create mode 100644 day14.swift

diff --git a/day14.swift b/day14.swift
new file mode 100644
index 0000000..692fa14
--- /dev/null
+++ b/day14.swift
@@ -0,0 +1,151 @@
+@main
+struct Day14 {
+    mutating func run() {
+        let part1 = calculate(start, depth: 10)
+        print("Part 1:", part1.values.max()! - part1.values.min()!)
+
+        let part2 = calculate(start, depth: 40)
+        print("Part 2:", part2.values.max()! - part2.values.min()!)
+    }
+
+    mutating func calculate(_ string: String, depth: Int) -> [Character: Int] {
+        var result: [Character: Int] = [:]
+        for (a, b) in zip(string, string.dropFirst()) {
+            result.merge(calculate(a, b, depth: depth), uniquingKeysWith: +)
+        }
+        result[string.last!, default: 0] += 1
+        return result
+    }
+
+    struct CacheKey: Hashable {
+        var string: String
+        var depth: Int
+    }
+    var cache: [CacheKey: [Character: Int]] = [:]
+
+    mutating func calculate(_ first: Character, _ second: Character, depth: Int) -> [Character: Int] {
+        guard depth > 0 else {
+            return [first: 1]
+        }
+
+        let pair = "\(first)\(second)"
+        let cacheKey = CacheKey(string: pair, depth: depth)
+
+        if let result = cache[cacheKey] {
+            return result
+        }
+
+        let mid = mapping[pair]!
+
+        var result = calculate(first, mid, depth: depth - 1)
+        result.merge(calculate(mid, second, depth: depth - 1), uniquingKeysWith: +)
+
+        cache[cacheKey] = result
+
+        return result
+    }
+
+    let start = "KBKPHKHHNBCVCHPSPNHF"
+    let mapping: [String: Character] = [
+        "OP": "H",
+        "CF": "C",
+        "BB": "V",
+        "KH": "O",
+        "CV": "S",
+        "FV": "O",
+        "FS": "K",
+        "KO": "C",
+        "PP": "S",
+        "SH": "K",
+        "FH": "O",
+        "NF": "H",
+        "PN": "P",
+        "BO": "H",
+        "OK": "K",
+        "PO": "P",
+        "SF": "K",
+        "BF": "P",
+        "HH": "S",
+        "KP": "H",
+        "HB": "N",
+        "NP": "V",
+        "KK": "P",
+        "PF": "P",
+        "BK": "V",
+        "OF": "H",
+        "FO": "S",
+        "VC": "P",
+        "FK": "B",
+        "NK": "S",
+        "CB": "B",
+        "PV": "C",
+        "CO": "N",
+        "BN": "C",
+        "HV": "H",
+        "OC": "N",
+        "NB": "O",
+        "CS": "S",
+        "HK": "C",
+        "VS": "F",
+        "BH": "C",
+        "PC": "S",
+        "KC": "O",
+        "VO": "P",
+        "FB": "K",
+        "BV": "V",
+        "VN": "N",
+        "ON": "F",
+        "VH": "H",
+        "CN": "O",
+        "HO": "O",
+        "SV": "O",
+        "SS": "H",
+        "KF": "N",
+        "SP": "C",
+        "NS": "V",
+        "SO": "F",
+        "BC": "P",
+        "HC": "C",
+        "FP": "H",
+        "OH": "S",
+        "OB": "S",
+        "HF": "V",
+        "SC": "B",
+        "SN": "N",
+        "VK": "C",
+        "NC": "V",
+        "VV": "S",
+        "SK": "K",
+        "PK": "K",
+        "PS": "N",
+        "KB": "S",
+        "KS": "C",
+        "NN": "C",
+        "OO": "C",
+        "BS": "B",
+        "NV": "H",
+        "FF": "P",
+        "FC": "N",
+        "OS": "H",
+        "KN": "N",
+        "VP": "B",
+        "PH": "N",
+        "NH": "S",
+        "OV": "O",
+        "FN": "V",
+        "CP": "B",
+        "NO": "V",
+        "CK": "C",
+        "VF": "B",
+        "HS": "B",
+        "KV": "K",
+        "VB": "H",
+        "SB": "S",
+        "BP": "S",
+        "CC": "F",
+        "HP": "B",
+        "PB": "P",
+        "HN": "P",
+        "CH": "O",
+    ]
+}