Day 14

day14/part1.py

@@ -0,0 +1,32 @@
+#!/usr/bin/env python3
+import re
+from collections import Counter
+
+lines = (x.strip() for x in open("input.txt"))
+first = next(lines)
+
+combinations = Counter(first[a:a+2] for a in range(len(first)-1))
+replacements = dict()
+
+next(lines)
+
+for line in lines:
+    before, insert = re.match(r"([A-Z]{2}) -> ([A-Z])", line).groups()
+    replacements[before] = (before[0]+insert, insert+before[1])
+
+for _ in range(10):
+    nxt = {}
+    for before, afters in replacements.items():
+        for after in afters:
+            add = combinations.get(before, 0) + nxt.get(after, 0)
+            if add:
+                nxt[after] = add
+    combinations = nxt
+
+letters = {}
+for key, cnt in combinations.items():
+    letters[key[0]] = letters.get(key[0], 0) + cnt
+    letters[key[1]] = letters.get(key[1], 0) + cnt
+
+print(letters)
+print((max(*letters.values())+1) // 2 - (min(*letters.values())+1) // 2)