2024 day 9.

src/holt59/aoc/2024/day9.py

@@ -4,4 +4,65 @@ from ..base import BaseSolver
 
 
 class Solver(BaseSolver):
-    def solve(self, input: str) -> Iterator[Any]: ...
+    def solve(self, input: str) -> Iterator[Any]:
+        blocks: list[tuple[int, int]] = []
+        frees: list[tuple[int, int]] = []
+
+        contents_0: list[int | None] = [None for _ in range(sum(map(int, input)))]
+
+        acc = 0
+        for i, c in enumerate(input):
+            if i % 2 == 0:
+                for j in range(acc, acc + int(c)):
+                    contents_0[j] = i // 2
+                blocks.append((acc, int(c)))
+            else:
+                frees.append((acc, int(c)))
+            acc += int(c)
+
+        assert contents_0[-1] is not None
+
+        contents = contents_0.copy()
+
+        free_0 = next(i for i, c in enumerate(contents) if c is None)
+        next_b = len(contents) - 1
+
+        while free_0 < next_b:
+            contents[free_0], contents[next_b] = contents[next_b], contents[free_0]
+
+            free_0 += 1
+            while free_0 < len(contents) and contents[free_0] is not None:
+                free_0 += 1
+
+            next_b -= 1
+            while next_b >= 0 and contents[next_b] is None:
+                next_b -= 1
+
+        yield sum(i * c for i, c in enumerate(contents) if c is not None)
+
+        contents = contents_0.copy()
+
+        for block_start, block_length in blocks[::-1]:
+            try:
+                i_free = next(
+                    i_free
+                    for i_free, (free_start, free_length) in enumerate(frees)
+                    if free_start < block_start and free_length >= block_length
+                )
+            except StopIteration:
+                continue
+
+            free_start, free_length = frees[i_free]
+
+            for i in range(block_length):
+                contents[free_start + i], contents[block_start + i] = (
+                    contents[block_start + i],
+                    None,
+                )
+
+            if free_length == block_length:
+                del frees[i_free]
+            else:
+                frees[i_free] = (free_start + block_length, free_length - block_length)
+
+        yield sum(i * c for i, c in enumerate(contents) if c is not None)

src/holt59/aoc/inputs/tests/2024/day9.txt

@@ -0,0 +1 @@
+2333133121414131402