69 lines
1.4 KiB
Python
69 lines
1.4 KiB
Python
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hmap = {}
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with open("input.txt") as f:
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lines = f.read().split('\n')
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height = len(lines)
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width = len(lines[0])
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for i, line in enumerate(lines):
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for j, n in enumerate(line):
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hmap[(i,j)] = int(n)
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def adjacent(i,j):
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adjacent = [
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(i-1,j),
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(i+1,j),
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(i,j-1),
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(i,j+1)
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]
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return [ (i,j) for (i,j) in adjacent if (-1 < i < height) and (-1 < j < width) ]
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# part 1
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lowpoints = []
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for i in range(height):
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for j in range(width):
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current = hmap[(i,j)]
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neighbors = [hmap[(x,y)] for (x,y) in adjacent(i,j)]
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if current < min(neighbors):
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lowpoints.append(current)
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risk = 0
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for h in lowpoints:
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risk += (h + 1)
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print(risk)
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# part 2
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basins = []
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allpoints = set(
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[ (i,j)
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for i in range(height)
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for j in range(width)
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]
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)
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def which_basin(i,j,hmap):
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"""
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Identifies the basin that (i,j) is part of.
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"""
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basin = set()
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visited = set()
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q = [(i,j)]
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while q:
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(x, y) = q.pop()
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if (x,y) not in visited:
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visited.add((x,y))
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if hmap[(x,y)] != 9:
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basin.add((x,y))
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neighbors = []
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q += [(m,n) for (m,n) in adjacent(x,y) if (m,n) not in visited]
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return basin
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identified = set()
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for i in range(height):
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for j in range(width):
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if (i,j) not in identified:
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basin = which_basin(i,j,hmap)
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for point in basin:
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identified.add(point)
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basins.append(basin)
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three_biggest_basins = sorted([len(basin) for basin in basins], reverse=True)[0:3]
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from math import prod
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part2 = prod(three_biggest_basins)
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print(part2)
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