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82 lines
2.0 KiB
Python
82 lines
2.0 KiB
Python
from dataclasses import dataclass
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from heapq import heappush, heappop
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DIRECTIONS = (
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1 + 0j, # EAST
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0 + 1j, # SOUTH
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-1 + 0j, # WEST
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0 - 1j, # NORTH
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)
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@dataclass(frozen=True)
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class Node:
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pos: complex
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cost: int = 0
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def __lt__(self, other):
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return self.cost < other.cost
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def can_reach(pos, obstacles, grid_size):
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height, width = grid_size
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x, y = int(pos.real), int(pos.imag)
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if 0 <= x < width and 0 <= y < height:
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if (x, y) not in obstacles:
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return True
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return False
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def search(obstacles, start, goal, grid_size): # could just use bfs?
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queue = [Node(start)]
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visited = set()
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i = 0
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while queue != []:
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node = heappop(queue)
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visited.add(node.pos)
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if node.pos == goal:
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return node.cost
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for direction in DIRECTIONS:
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new_pos = node.pos + direction
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n = Node(new_pos, node.cost + 1)
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if n not in queue and n.pos not in visited and can_reach(n.pos, obstacles, grid_size):
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heappush(queue, n)
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return -1
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def find_path(coords, limit, grid_size):
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obstacles = coords[:limit]
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start = 0+0j
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goal = complex(grid_size[0] - 1, grid_size[1] - 1)
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cost = search(obstacles, start, goal, grid_size)
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return cost
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def main(coords, limit, grid_size):
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part1 = find_path(coords, limit, grid_size)
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print("Part 1: ", part1)
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# binary search for part 2
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low, high = limit, len(coords)
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while high - low > 1:
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i = (low + high) // 2
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if find_path(coords, i, grid_size) != -1:
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low = i
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else:
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high = i
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print("Part 2: ", coords[low])
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if __name__ == "__main__":
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import sys
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infile = sys.argv[1] if len(sys.argv) > 1 else "example.txt"
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with open(infile) as f:
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lines = f.readlines()
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lines = [tuple(map(int, l.rstrip().split(","))) for l in lines]
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if infile == "example.txt":
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main(lines, 12, (7, 7))
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else:
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main(lines, 1024, (71, 71))
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