2023 day 3 part 2 (incorrect)

Author: BioGeek

2023/day03.py

@@ -1,39 +1,101 @@
 import re
+from collections import namedtuple
+from itertools import combinations
 
+Point = namedtuple("Point", ["x", "y"])
+BoundingBox = namedtuple("BoundingBox", ["bottom_left", "top_right"])
 
-def part_number_count(schematic):
+
+def intersects(bbox_a, bbox_b):
+    # Adapted from https://stackoverflow.com/a/40795835
+    return not (
+        bbox_a.top_right.x < bbox_b.bottom_left.x
+        or bbox_a.bottom_left.x > bbox_b.top_right.x
+        or bbox_a.top_right.y > bbox_b.bottom_left.y
+        or bbox_a.bottom_left.y < bbox_b.top_right.y
+    )
+
+
+def overlapping_content(bbox_a, bbox_b, rows):
+    # Calculate the max bounding box
+    # x_start = min(bbox_a.bottom_left.x, bbox_b.bottom_left.x)
+    # x_end = max(bbox_a.top_right.x, bbox_b.top_right.x)
+    # y_start = min(bbox_a.top_right.y, bbox_b.top_right.y)
+    # y_end = max(bbox_a.bottom_left.y, bbox_b.bottom_left.y)
+    #
+    # overlapping_text = []
+    # for y in range(y_start, y_end + 1):
+    #     row_content = rows[y]
+    #     overlapping_text.append(row_content[x_start : x_end + 1])
+    # print("\n".join(overlapping_text))
+
+    # Calculate the overlapping region
+    x_start = max(bbox_a.bottom_left.x, bbox_b.bottom_left.x)
+    x_end = min(bbox_a.top_right.x, bbox_b.top_right.x)
+    y_start = max(bbox_a.top_right.y, bbox_b.top_right.y)
+    y_end = min(bbox_a.bottom_left.y, bbox_b.bottom_left.y)
+
+    overlapping_text = []
+    for y in range(y_start, y_end + 1):
+        row_content = rows[y]
+        overlapping_text.append(row_content[x_start : x_end + 1])
+    return "\n".join(overlapping_text)
+
+
+def part_number_count(schematic, part=1):
     part_numbers = 0
     rows = schematic.splitlines()
     width = len(rows[0])
     new_rows = ["." * (width + 2)] + [f".{row}." for row in rows] + ["." * (width + 2)]
-    # print('\n'.join(new_rows))
+
+    bounding_boxes = {}
     for row_nr, line in enumerate(new_rows):
         matches = re.finditer(r"\d+", line)
         for match in matches:
             number = int(match.group())
             start = match.start()
             end = match.end()  # End position (exclusive)
-            # print(f"Number: {number}, Start: {start}, End: {end}, row nr {row_nr}")
 
-            symbols = []
             position_before = start - 1
-            symbols.append(new_rows[row_nr][position_before])
             position_after = end
-            symbols.append(new_rows[row_nr][position_after])
             row_nr_above = row_nr - 1
-            symbols.extend(new_rows[row_nr_above][position_before : position_after + 1])
             row_nr_below = row_nr + 1
+
+            symbols = []
+            symbols.append(new_rows[row_nr][position_before])
+            symbols.append(new_rows[row_nr][position_after])
+            symbols.extend(new_rows[row_nr_above][position_before : position_after + 1])
             symbols.extend(new_rows[row_nr_below][position_before : position_after + 1])
-            # print(set(symbols))
+
             if len(set(symbols)) > 1:
                 part_numbers += number
-    return part_numbers
+
+            if part == 2:
+                if "*" in symbols:
+                    bottom_left = Point(position_before, row_nr_below)
+                    top_right = Point(position_after, row_nr_above)
+                    bounding_boxes[number] = BoundingBox(bottom_left, top_right)
+
+    if part == 1:
+        return part_numbers
+    else:
+        gear_ratio = 0
+        for part_number_a, part_number_b in combinations(
+            sorted(bounding_boxes.keys()), 2
+        ):
+            bbox_a = bounding_boxes[part_number_a]
+            bbox_b = bounding_boxes[part_number_b]
+            if intersects(bbox_a, bbox_b) and "*" in overlapping_content(
+                bbox_a, bbox_b, new_rows
+            ):
+                gear_ratio += part_number_a * part_number_b
+        return gear_ratio
 
 
 def main(part: int = 1) -> int:
     with open("2023/data/day03.txt") as f:
         schematic = f.read()
-    return part_number_count(schematic)
+    return part_number_count(schematic, part)
 
 
 if __name__ == "__main__":
@@ -51,3 +113,7 @@ def main(part: int = 1) -> int:
     assert part_number_count(schematic) == 4361
 
     print(main())
+
+    assert part_number_count(schematic, part=2) == 467835
+
+    print(main(part=2))