58 lines
1.8 KiB
Python
58 lines
1.8 KiB
Python
def parse_input(input: list[str]):
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l = [(x, y) for (y, line) in enumerate(input) for (x, c) in enumerate(line) if c == '#']
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start = [(x, y) for (y, line) in enumerate(input) for (x, c) in enumerate(line) if c == 'S'][0]
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goal = [(x, y) for (y, line) in enumerate(input) for (x, c) in enumerate(line) if c == 'E'][0]
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w = max([x for (x, y) in l])
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h = max([y for (x, y) in l])
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return l, w, h, start, goal
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def sssp(points, w, h, start):
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visited = dict()
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(sx, sy) = start
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stack = [(sx, sy, 0)]
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while len(stack) > 0:
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(x, y, c) = stack.pop(0)
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if (x, y) in visited:
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continue
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visited[(x, y)] = c
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for (a, b) in [(x+nx, y+ny) for (nx, ny) in [(0, 1), (1, 0), (0, -1), (-1, 0)]]:
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if 0 <= a <= w and 0 <= b <= w and (a, b) not in points:
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stack.append((a, b, c + 1))
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return visited
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def mhd(a, b):
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(xa, ya) = a
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(xb, yb) = b
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return abs(xa - xb) + abs(ya - yb)
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def others(origin, max_distance):
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(sx, sy) = origin
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return [(a, b) for a in range(sx - max_distance, sx + max_distance + 1) for b in range(sy - max_distance, sy + max_distance + 1)]
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def solve(points, threshold, cheat_length):
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fromstart = sssp(set(points), w, h, start)
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toend = sssp(set(points), w, h, goal)
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cheatrange = range(2, cheat_length + 1)
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return len([1 for a in fromstart for b in others(a, cheat_length) if mhd(a, b) in cheatrange and b in toend and fromstart[a] + mhd(a, b) + toend[b] <= threshold])
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source = "input/day20.txt"
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with open(source, 'r') as f:
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data = f.read()
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(points, w, h, start, goal) = parse_input(data.strip().split('\n'))
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bottomline = sssp(set(points), w, h, start)[goal]
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solution1 = solve(set(points), bottomline - 100, 2)
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print("part 1: " + str(solution1))
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solution2 = solve(set(points), bottomline - 100, 20)
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print("part 2: " + str(solution2))
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