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84 lines
2.0 KiB
Python
84 lines
2.0 KiB
Python
from dataclasses import dataclass
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from collections import defaultdict
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@dataclass(frozen=True)
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class Vec2d:
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x: int
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y: int
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def __add__(self, other):
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return Vec2d(self.x + other.x, self.y + other.y)
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DIRECTIONS = (
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Vec2d(0, -1), # N
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Vec2d(1, 0), # E
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Vec2d(0, 1), # S
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Vec2d(-1, 0), # W
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)
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def in_bounds(grid, pos):
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return 0 <= pos.y < len(grid) and 0 <= pos.x < len(grid[0])
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def visit_region(grid, root):
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region = set()
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# BFS
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queue = [root]
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visited = set()
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region.add(root)
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visited.add(root)
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while queue != []:
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node = queue.pop(0)
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for d in DIRECTIONS:
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new_pos = node + d
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if in_bounds(grid, new_pos) and new_pos not in visited:
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visited.add(new_pos)
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if grid[root.y][root.x] == grid[new_pos.y][new_pos.x]:
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queue.append(new_pos)
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region.add(new_pos)
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return region
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def get_perimeter(grid, region):
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perimeter = 0
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for node in region:
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for d in DIRECTIONS:
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new_pos = node + d
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if not in_bounds(grid, new_pos) or grid[new_pos.y][new_pos.x] != grid[node.y][node.x]:
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perimeter += 1
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return perimeter
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def main(grid):
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# build list of regions using BFS
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regions = []
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visited = set()
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for y, row in enumerate(grid):
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for x, c in enumerate(row):
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pos = Vec2d(x, y)
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if pos not in visited:
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region = visit_region(grid, pos)
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visited.update(region)
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regions.append((c, region))
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total = 0
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for region in regions:
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c, nodes = region
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area = len(nodes)
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perimeter = get_perimeter(grid, nodes)
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#print(f"Region {c} area {area} perimeter {perimeter}")
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total += area * perimeter
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print("Part 1: ", total)
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if __name__ == "__main__":
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import sys
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infile = sys.argv[1] if 1 < len(sys.argv) else "example.txt"
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with open(infile) as f:
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grid = [l.rstrip() for l in f.readlines()]
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main(grid)
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