Refactor 2025 day 6 to transpose text

Author: Peter554

2025/python/src/aoc2025/day06.py

@@ -1,3 +1,4 @@
+import itertools
 import math
 from pathlib import Path
 
@@ -27,34 +28,30 @@ def part_1(input: Path) -> int:
 
 
 def part_2(input: Path) -> int:
-    text = [[c for c in line] for line in input.read_text().splitlines()]
-    len_longest_line = max(len(line) for line in text)
-    text = [line + [" "] * (len_longest_line - len(line)) for line in text]
+    text = transpose_text(input.read_text())
 
     answers = []
     this_problem_numbers = []
-    for col in range(len(text[0]) - 1, -1, -1):
-        number: int | None = None
-        operator: str | None = None
-        for row in range(len(text)):
-            char = text[row][col]
-            if char.isnumeric():
-                if number is None:
-                    number = int(char)
-                else:
-                    number = 10 * number + int(char)
-            elif char != " ":
-                operator = char
-        if number is not None:
-            this_problem_numbers.append(number)
-        if operator is not None:
-            match operator:
+    for line in reversed(text.splitlines()):
+        if not line:
+            continue
+        if line.endswith("+") or line.endswith("*"):
+            this_problem_numbers.append(int(line[:-1]))
+            match line[-1]:
                 case "+":
                     answers.append(sum(this_problem_numbers))
                 case "*":
                     answers.append(math.prod(this_problem_numbers))
                 case _:
-                    raise ValueError(f"Invalid operator: {operator}")
+                    raise ValueError(f"Invalid operator: {line[-1]}")
             this_problem_numbers = []
+        else:
+            this_problem_numbers.append(int(line))
 
     return sum(answers)
+
+
+def transpose_text(s: str) -> str:
+    lines = s.splitlines()
+    transposed_lines = itertools.zip_longest(*lines, fillvalue=" ")
+    return "\n".join("".join(line).rstrip() for line in transposed_lines)

2025/python/tests/test_day06.py

@@ -5,6 +5,19 @@
 DATA_DIR = Path(__file__).parent.parent / "data/day06"
 
 
+def test_transpose_text():
+    assert (
+        day06.transpose_text("""\
+ab
+cde
+ f""")
+        == """\
+ac
+bdf
+ e"""
+    )
+
+
 def test_part_1(benchmark):
     assert day06.part_1(DATA_DIR / "example.txt") == 4277556
     assert benchmark(lambda: day06.part_1(DATA_DIR / "input.txt")) == 3525371263915