Solve 2021 day 12-14

2021/d14.py

@@ -0,0 +1,43 @@
+from lib import get_data
+from itertools import pairwise
+from collections import defaultdict
+
+data = get_data(__file__)
+orig_t, p2 = data.split("\n\n")
+
+pairs = {}
+for line in p2.splitlines():
+    ls, rs = line.split(" -> ")
+    assert ls not in pairs
+    pairs[ls] = rs
+
+for steps in [10, 40]:
+    t = str(orig_t)
+    start_letter = t[0]
+    end_letter = t[-1]
+    td = defaultdict(int)
+    for a, b in pairwise(t):
+        td[a + b] += 1
+
+    for _ in range(steps):
+        ntd = defaultdict(int)
+        for pair, count in td.items():
+            if pair in pairs:
+                a, b = pair
+                c = pairs[pair]
+                ntd[a + c] += count
+                ntd[c + b] += count
+            else:
+                ntd[pair] += count
+        td = ntd
+
+    counts = defaultdict(int)
+    for (a, b), count in td.items():
+        counts[a] += count
+        counts[b] += count
+    counts = {k: v // 2 for k, v in counts.items()}
+    counts[start_letter] += 1
+    counts[end_letter] += 1
+
+    r = max(counts.values()) - min(counts.values())
+    print(r)