Add solution to 2024-12-09

Author: fuglede

2024/day09/solutions.py

@@ -0,0 +1,44 @@
+with open("input") as f:
+    ns = list(map(int, f.read().strip()))
+
+# Part 1
+disk = []
+for i, n in enumerate(ns):
+    disk += [None if i % 2 else i // 2] * n
+
+head = ns[0]
+while head < len(disk):
+    if disk[head]:
+        head += 1
+    elif num := disk.pop():
+        disk[head] = num
+
+print(sum(i * n for i, n in enumerate(disk)))
+
+# Part 2
+blocks = []
+head = 0
+for i, n in enumerate(ns):
+    if not i % 2:
+        blocks.append((i // 2, head, head + n))
+    head += n
+
+for to_move in range(i // 2, -1, -1):
+    block = next(b for b in blocks if b[0] == to_move)
+    _, start, end = block
+    space_needed = end - start
+    for i, ((_, _, end1), (_, start2, _)) in enumerate(zip(blocks, blocks[1:])):
+        if end1 == end:
+            break
+        if start2 - end1 >= space_needed:
+            blocks.insert(i + 1, (to_move, end1, end1 + space_needed))
+            blocks.remove(block)
+            break
+
+print(
+    sum(
+        block_id * index
+        for block_id, start, end in blocks
+        for index in range(start, end)
+    )
+)