2023 day 12 part 1

README.md

@@ -14,7 +14,7 @@
 - 2020 - ★★★★★ ★★★★★ ★★★★★ ☆
 - 2021 - ★★★★★ ★★★★★ ★★★★★ ★★★
 - 2022 - ★★★★★ ★★★★★ ★★★★★ ★☆
-- 2023 - ★★★★☆ ★☆★★☆ ★
+- 2023 - ★★★★☆ ★☆★★☆ ★☆
 
 ## How to use
 

src/year2023/day12a.py

@@ -0,0 +1,58 @@
+"""2023 - Day 12 Part 1: Hot Springs"""
+from dataclasses import dataclass
+from typing import Self
+
+
+@dataclass
+class Row:
+    springs: str
+    segments: list[int]
+
+    @property
+    def arrangements(self) -> int:
+        n = len(self.segments)
+
+        def dfs(i: int, j: int, filled: int) -> int:
+            if i == len(self.springs):
+                if (j == n and filled == 0) or (
+                    j == n - 1 and filled == self.segments[j]
+                ):
+                    return 1
+                else:
+                    return 0
+
+            count = 0
+
+            if self.springs[i] in {".", "?"}:
+                if filled == 0:
+                    count += dfs(i + 1, j, filled)
+                elif filled == self.segments[j]:
+                    count += dfs(i + 1, j + 1, 0)
+
+            if self.springs[i] in {"#", "?"}:
+                if j < n and filled < self.segments[j]:
+                    count += dfs(i + 1, j, filled + 1)
+
+            return count
+
+        return dfs(0, 0, 0)
+
+    @classmethod
+    def from_line(cls, line: str) -> Self:
+        springs, segments_part = line.split()
+        segments = [int(x) for x in segments_part.split(",")]
+        return cls(springs, segments)
+
+
+@dataclass
+class Field:
+    rows: list[Row]
+
+    @classmethod
+    def from_task(cls, task: str) -> Self:
+        return cls([Row.from_line(line) for line in task.splitlines()])
+
+
+def solve(task: str) -> int:
+    field = Field.from_task(task)
+    return sum(r.arrangements for r in field.rows)

tests/src/year2023/test_day12a.py

@@ -0,0 +1,36 @@
+"""2023 - Day 12 Part 1: Hot Springs"""
+from textwrap import dedent
+
+import pytest
+
+from src.year2023.day12a import Row
+from src.year2023.day12a import solve
+
+
+@pytest.mark.parametrize(
+    "line,expected",
+    (
+        ("???.### 1,1,3", 1),
+        (".??..??...?##. 1,1,3", 4),
+        ("?#?#?#?#?#?#?#? 1,3,1,6", 1),
+        ("????.#...#... 4,1,1", 1),
+        ("????.######..#####. 1,6,5", 4),
+        ("?###???????? 3,2,1", 10),
+    ),
+)
+def test_row(line, expected):
+    assert Row.from_line(line).arrangements == expected
+
+
+def test_solve():
+    task = dedent(
+        """
+        ???.### 1,1,3
+        .??..??...?##. 1,1,3
+        ?#?#?#?#?#?#?#? 1,3,1,6
+        ????.#...#... 4,1,1
+        ????.######..#####. 1,6,5
+        ?###???????? 3,2,1
+        """
+    ).strip()
+    assert solve(task) == 21