68 lines
1.6 KiB
Python
68 lines
1.6 KiB
Python
import heapq
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from lib import get_data
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from lib import ints
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from lib import Grid2D
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data = get_data(__file__)
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size = 71
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grid = "\n".join(["." * size for _ in range(size)])
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g = Grid2D(grid)
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for i, line in enumerate(data.splitlines()):
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x, y = ints(line)
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g[(y, x)] = "x"
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start = (0, 0)
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end = (size - 1, size - 1)
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def dist(n1, n2):
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"""cost from node to node"""
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if n1 == 0 or n1 == n2:
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return 0
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return 1
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def h(node):
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"""heuristic function (never overestimate)"""
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return abs(node[0] - end[0]) + abs(node[1] - end[1])
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def is_goal(node):
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return node == end
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def neighbors(node):
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nbs = []
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for nb in g.neighbors_ort(node):
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if g[nb] != "x":
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nbs.append(nb)
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return nbs
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starts = [start]
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open_set = []
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g_score = {}
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cost = None
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for start in starts:
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heapq.heappush(open_set, (h(start), start))
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g_score[start] = dist(0, start)
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while open_set:
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current_f_score, current = heapq.heappop(open_set)
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if is_goal(current):
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assert current_f_score == g_score[current]
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cost = g_score[current]
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break
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for neighbor in neighbors(current):
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tentative_g_score = g_score[current] + dist(current, neighbor)
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if neighbor not in g_score or tentative_g_score < g_score[neighbor]:
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g_score[neighbor] = tentative_g_score
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f_score = g_score[neighbor] + h(neighbor)
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heapq.heappush(open_set, (f_score, neighbor))
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if i == 1023:
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print(cost)
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if cost is None:
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print(line)
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break
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