14

2021/14/README.md

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+# 14
+
+This was nice! Similar to the Lanterfish one. The naive way is to have a big string, but that becomes unfeasible quickly.
+
+The solution was to keep track of the number of combinations available and at the end divide by 2 the counted elements. Rounding up so that the first and last element is not neglected as they are not doubled.
+
+<details>
+  <summary>Solutions</summary>
+  <ol>
+    <li>2988</li>
+    <li>3572761917024</li>
+  </ol>
+</details>

2021/14/input.txt

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+VFHKKOKKCPBONFHNPHPN
+
+VS -> B
+HK -> B
+FO -> P
+NC -> F
+VN -> C
+BS -> O
+HS -> K
+NS -> C
+CV -> P
+NV -> C
+PH -> H
+PB -> B
+PK -> K
+HF -> P
+FV -> C
+NN -> H
+VO -> K
+VP -> P
+BC -> B
+KK -> S
+OK -> C
+PN -> H
+SB -> V
+KO -> P
+KH -> C
+KS -> S
+FP -> B
+PV -> B
+BO -> C
+OS -> H
+NB -> S
+SP -> C
+HN -> N
+FN -> B
+PO -> O
+FS -> O
+NH -> B
+SO -> P
+OB -> S
+KC -> C
+OO -> H
+BB -> V
+SC -> F
+NP -> P
+SH -> C
+BH -> O
+BP -> F
+CC -> S
+BN -> H
+SS -> P
+BF -> B
+VK -> P
+OV -> H
+FC -> S
+VB -> S
+PF -> N
+HH -> O
+HC -> V
+CH -> B
+HP -> H
+FF -> H
+VF -> V
+CS -> F
+KP -> F
+OP -> H
+KF -> F
+PP -> V
+OC -> C
+PS -> F
+ON -> H
+BK -> B
+HV -> S
+CO -> K
+FH -> C
+FB -> F
+OF -> V
+SN -> S
+PC -> K
+NF -> F
+NK -> P
+NO -> P
+CP -> P
+CK -> S
+HB -> H
+BV -> C
+SF -> K
+HO -> H
+OH -> B
+KV -> S
+KN -> F
+SK -> K
+VH -> S
+CN -> S
+VC -> P
+CB -> H
+SV -> S
+VV -> P
+CF -> F
+FK -> F
+KB -> V
+

2021/14/python/main.py

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+#!/usr/bin/env python
+
+import math
+from collections import defaultdict
+from os.path import dirname, join
+
+# Day 14
+
+# Common
+
+
+def read_input(filename):
+    data = join(dirname(__file__), '..', filename)
+    with open(data) as f:
+        return f.read().strip()
+
+
+test = read_input('test.txt')
+data = read_input('input.txt')
+
+
+class Polymer:
+    def __init__(self, state: str, insertions: dict[str, str]):
+        self.state = state
+        self.insertions = insertions
+        self.states: defaultdict[str, int] = defaultdict(lambda: 0)
+
+        for i in range(len(self) - 1):
+            pair = self.state[i:i+2]
+            self.states[pair] += 1
+
+    def __len__(self):
+        return len(self.state)
+
+    def step(self):
+        new = defaultdict(lambda: 0)
+        for state, count in self.states.items():
+            if count == 0:
+                continue
+            insertion = self.insertions[state]
+            for key in [state[0] + insertion, insertion + state[1]]:
+                new[key] += count
+        self.states = new
+
+    def score(self):
+        elements = defaultdict(lambda: 0)
+        for state, count in self.states.items():
+            for element in state:
+                elements[element] += count
+        for element, count in elements.items():
+            elements[element] = math.ceil(elements[element]/2)
+        return max(elements.values()) - min(elements.values())
+
+    def flag(self, steps: int):
+        for _ in range(steps):
+            self.step()
+        print(self.score())
+
+    @staticmethod
+    def parse(data: str):
+        state, raw = data.split('\n\n')
+        lines = [
+            l.split(' -> ')
+            for l in raw.split('\n')
+        ]
+        insertions = {
+            i[0]: i[1]
+            for i in lines
+        }
+        return Polymer(state.strip(), insertions)
+
+
+# 1
+print('1.')
+
+polymer = Polymer.parse(test)
+polymer.flag(10)
+polymer = Polymer.parse(data)
+polymer.flag(10)
+
+# 2
+print('\n2.')
+polymer = Polymer.parse(test)
+polymer.flag(40)
+polymer = Polymer.parse(data)
+polymer.flag(40)

2021/14/test.txt

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+NNCB
+
+CH -> B
+HH -> N
+CB -> H
+NH -> C
+HB -> C
+HC -> B
+HN -> C
+NN -> C
+BH -> H
+NC -> B
+NB -> B
+BN -> B
+BB -> N
+BC -> B
+CC -> N
+CN -> C