2021 Day 14

2021/14/code.py

@@ -0,0 +1,48 @@
+# SPDX-License-Identifier: MIT
+# Copyright (c) 2021 Akumatic
+#
+# https://adventofcode.com/2021/day/14
+
+def read_file(filename: str = "input.txt") -> tuple:
+    with open(f"{__file__.rstrip('code.py')}{filename}", "r") as f:
+        lines = [line for line in f.read().strip().split("\n")]
+    template = lines[0]
+    rules = {x[0]: x[1] for x in (line.split(" -> ") for line in lines[2:])}
+    return template, rules
+
+def add_to_dict(d: dict, key: str, val: int = 1):
+    if key not in d:
+        d[key] = val
+    else:
+        d[key] += val
+
+def count(polymer: str, rules: dict, iterations: int) -> dict:
+    pairs = dict()
+    for i in range(len(polymer) - 1):
+        add_to_dict(pairs, polymer[i] + polymer[i+1])
+
+    for _ in range(iterations):
+        tmp = dict()
+        for pair in pairs:
+            add_to_dict(tmp, pair[0] + rules[pair], pairs[pair])
+            add_to_dict(tmp, rules[pair] + pair[1], pairs[pair])
+        pairs = tmp
+
+    elements = dict()
+    for pair in pairs:
+        add_to_dict(elements, pair[0], pairs[pair])
+    add_to_dict(elements, polymer[-1])
+    return elements
+
+def part1(template: str, insertion_rules: dict) -> int:
+    letters = count(template, insertion_rules, 10)
+    return max(letters.values()) - min(letters.values())
+
+def part2(template: str, insertion_rules: dict) -> int:
+    letters = count(template, insertion_rules, 40)
+    return max(letters.values()) - min(letters.values())
+    
+if __name__ == "__main__":
+    vals = read_file() # vals[0] is the template, vals[1] the insertion rules
+    print(f"Part 1: {part1(*vals)}")
+    print(f"Part 2: {part2(*vals)}")