AoC 2025 Day 3

Author: pareronia

README.md

@@ -8,7 +8,7 @@
 <!-- @BEGIN:ImplementationsTable:2025@ -->
 | | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
 | ---| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
-| python3 | [✓](src/main/python/AoC2025_01.py) | [✓](src/main/python/AoC2025_02.py) |  |  |  |  |  |  |  |  |  |  |
+| python3 | [✓](src/main/python/AoC2025_01.py) | [✓](src/main/python/AoC2025_02.py) | [✓](src/main/python/AoC2025_03.py) |  |  |  |  |  |  |  |  |  |
 | java | [✓](src/main/java/AoC2025_01.java) | [✓](src/main/java/AoC2025_02.java) |  |  |  |  |  |  |  |  |  |  |
 | bash | [✓](src/main/bash/AoC2025_01.sh) | [✓](src/main/bash/AoC2025_02.sh) |  |  |  |  |  |  |  |  |  |  |
 <!-- @END:ImplementationsTable:2025@ -->

src/main/python/AoC2025_03.py

@@ -0,0 +1,106 @@
+#! /usr/bin/env python3
+#
+# Advent of Code 2025 Day 3
+#
+
+import sys
+from functools import cache
+
+from aoc.common import InputData
+from aoc.common import SolutionBase
+from aoc.common import aoc_samples
+from aoc.common import log
+
+Input = InputData
+Output1 = int
+Output2 = int
+
+
+TEST = """\
+987654321111111
+811111111111119
+234234234234278
+818181911112111
+"""
+
+
+class Solution(SolutionBase[Input, Output1, Output2]):
+    def parse_input(self, input_data: InputData) -> Input:
+        return input_data
+
+    def part_1(self, inputs: Input) -> Output1:
+        ans = 0
+        for line in inputs:
+            first = max(enumerate(line[:-1]), key=lambda e: (e[1], -e[0]))
+            second = max(
+                enumerate(line[first[0] + 1 :]), key=lambda e: (e[1], -e[0])
+            )
+            ans += int(first[1] + second[1])
+        return ans
+
+    def part_2(self, inputs: Input) -> Output2:
+        @cache
+        def dfs(left: int, start: int) -> int:
+            if start >= len(line):
+                return 0
+            if left == 1:
+                if start == len(line) - 1:
+                    return int(line[-1])
+                return max(int(line[start]), dfs(1, start + 1))
+            cur = dfs(left - 1, start + 1)
+            nxt = dfs(left, start + 1)
+            if cur > 0:
+                return max(int(line[start] + str(cur)), nxt)
+            return nxt
+
+        dfs.cache_clear()
+        line = "1"
+        test = dfs(1, 0)
+        assert test == 1, test
+        dfs.cache_clear()
+        line = "21"
+        test = dfs(1, 0)
+        assert test == 2, test
+        dfs.cache_clear()
+        line = "12"
+        test = dfs(1, 0)
+        assert test == 2, test
+        dfs.cache_clear()
+        line = "12"
+        test = dfs(2, 0)
+        assert test == 12, test
+        dfs.cache_clear()
+        line = "123"
+        test = dfs(2, 0)
+        assert test == 23, test
+        dfs.cache_clear()
+        line = "321"
+        test = dfs(2, 0)
+        assert test == 32, test
+        ans = 0
+        for line in inputs:  # noqa:B007
+            dfs.cache_clear()
+            best = dfs(12, 0)
+            log(best)
+            ans += best
+        return ans
+
+    @aoc_samples(
+        (
+            ("part_1", TEST, 357),
+            ("part_2", TEST, 3121910778619),
+        )
+    )
+    def samples(self) -> None:
+        pass
+
+
+solution = Solution(2025, 3)
+
+
+def main() -> None:
+    solution.run(sys.argv)
+
+
+if __name__ == "__main__":
+    main()