Added day9

day9/example.txt

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+2333133121414131402

day9/output.txt

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+0099811188827773336446555566

day9/solution.py

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+import sys
+
+def main():
+    raw_line = sys.stdin.read().strip()
+    line = [int(x) for x in raw_line]
+
+    files_map = []
+    file_id = 0
+    is_file_len = True
+    for num in line:
+        if is_file_len:
+            if num > 0:
+                files_map.extend([str(file_id)] * num)
+                file_id += 1
+        else:
+            if num > 0:
+                files_map.extend(["."] * num)
+        is_file_len = not is_file_len
+
+    map_list = files_map
+    while True:
+        try:
+            gap_index = map_list.index(".")
+        except ValueError:
+            break
+        if all(x == "." for x in map_list[gap_index+1:]):
+            break
+        rightmost_file_index = None
+        for idx in range(len(map_list)-1, -1, -1):
+            if map_list[idx] != ".":
+                rightmost_file_index = idx
+                break
+        map_list[gap_index] = map_list[rightmost_file_index]
+        map_list[rightmost_file_index] = "."
+
+    checksum_parts = []
+    for idx, val in enumerate(map_list):
+        if val != ".":
+            checksum_parts.append(idx * int(val))
+    print("System Checksum Found: " + str(sum(checksum_parts)))
+
+if __name__ == "__main__":
+    main()

day9/solution2.py

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+import sys
+
+def main():
+    raw_line = sys.stdin.read().strip()
+    line = [int(x) for x in raw_line]
+
+    blocks = []
+    file_id = 0
+    is_file_len = True
+    for num in line:
+        if is_file_len:
+            if num > 0:
+                blocks.extend([str(file_id)] * num)
+                file_id += 1
+        else:
+            if num > 0:
+                blocks.extend(["."] * num)
+        is_file_len = not is_file_len
+
+    # Move whole files in order of decreasing file ID
+    max_file_id = file_id - 1
+    for fid in range(max_file_id, -1, -1):
+        file_positions = [i for i, b in enumerate(blocks) if b == str(fid)]
+        if not file_positions:
+            continue
+        file_len = len(file_positions)
+        leftmost_file_index = min(file_positions)
+
+        candidate_spans = []
+        free_count = 0
+        start_index = 0
+        for i in range(leftmost_file_index):
+            if blocks[i] == '.':
+                if free_count == 0:
+                    start_index = i
+                free_count += 1
+                if free_count == file_len:
+                    candidate_spans.append((start_index, i))
+            else:
+                free_count = 0
+
+        if not candidate_spans:
+            continue
+
+        span_start, span_end = candidate_spans[0]
+
+        for pos in file_positions:
+            blocks[pos] = '.'
+        for i in range(span_start, span_start + file_len):
+            blocks[i] = str(fid)
+
+    # Compute checksum
+    checksum_parts = []
+    for idx, val in enumerate(blocks):
+        if val != ".":
+            checksum_parts.append(idx * int(val))
+    print("System Checksum Found: " + str(sum(checksum_parts)))
+
+if __name__ == "__main__":
+    main()