Day 12

day12.py

@@ -0,0 +1,80 @@
+#!/usr/bin/env python
+
+# https://adventofcode.com/2025/day/12
+
+import re
+
+
+def prep_data(filename):
+  shape_re = re.compile(r"\d:")
+  region_re = re.compile(r"\d+x\d+:")
+  shapes, regions, quantities = {}, [], []
+
+  f = open(filename, "r")
+  lines = [l.rstrip("\n") for l in f.readlines()]
+  f.close()
+
+  while lines != []:
+    line = lines.pop(0)
+
+    # shape
+    if shape_re.match(line):
+      tmp = []
+      # read shape lines
+      while True:
+        l = lines.pop(0)
+        if l == "":
+          break
+        else: 
+          tmp.append(l)
+
+      # parse shape
+      shape = []
+      for i in range(len(tmp)):
+        for j in range(len(tmp[0])):
+          if tmp[i][j] == "#":
+            shape.append((i, j))
+      shapes["shape-" + line[:-1]] = shape
+      
+    # region & quantities
+    elif region_re.match(line):
+      tmp = line.split(" ")
+      regions.append(list(map(int, tmp.pop(0)[:-1].split("x"))))
+      quantities.append(list(map(int, tmp)))
+
+  return shapes, regions, quantities    
+
+
+def solve_part_1() -> int:
+  shapes, regions, quantities = prep_data("day12input.txt")
+  areas = [len(shape) for shape in shapes]
+
+  solvable, unsolvable, dont_know = 0, 0, 0
+
+  # loop over problems
+  for i in range(len(regions)):
+    board = regions[i]
+    quantity = quantities[i]
+    
+    # simple solvability check
+    if board[0] * board[1] < sum(list(map(lambda a, q: a * q, areas, quantity))):
+      print(f"Problem {i} is unsolvable")
+      unsolvable += 1
+
+    # check if a tileset of 3x3 squares would fit in theory
+    elif (board[0] // 3) * (board[1] // 3) >= sum(quantity):
+      print(f"Problem {i} is solvable")
+      solvable += 1 
+      
+    else:
+      print(f"don't know about problem {i}")
+      dont_know += 1
+
+  print(f"{solvable=}")
+  print(f"{unsolvable=}")
+  print(f"{dont_know=}")
+  return solvable
+
+
+# solve part 1
+print(solve_part_1())