132 lines
3.4 KiB
Python
132 lines
3.4 KiB
Python
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# -*- encoding: utf-8 -*-
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import heapq
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import sys
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def dijkstra(
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start: tuple[int, int], end: tuple[int, int], grid: list[list[int]]
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) -> list[tuple[int, int]] | None:
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n_rows = len(grid)
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n_cols = len(grid[0])
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def heuristic(row: int, col: int) -> int:
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return abs(end[0] - row) + abs(end[1] - col)
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queue: list[tuple[tuple[int, int], tuple[int, int]]] = []
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visited: set[tuple[int, int]] = set()
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lengths: dict[tuple[int, int], int] = {}
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parents: dict[tuple[int, int], tuple[int, int]] = {}
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heapq.heappush(queue, ((heuristic(start[0], start[1]), 0), start))
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while queue:
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(_, length), (c_row, c_col) = heapq.heappop(queue)
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visited.add((c_row, c_col))
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if (c_row, c_col) == end:
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break
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for n_row, n_col in (
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(c_row - 1, c_col),
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(c_row + 1, c_col),
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(c_row, c_col - 1),
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(c_row, c_col + 1),
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):
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if not (n_row >= 0 and n_row < n_rows and n_col >= 0 and n_col < n_cols):
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continue
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if (n_row, n_col) in visited:
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continue
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if grid[n_row][n_col] > grid[c_row][c_col] + 1:
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continue
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if length + 1 < lengths.get((n_row, n_col), n_rows * n_cols):
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lengths[n_row, n_col] = length + 1
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parents[n_row, n_col] = (c_row, c_col)
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heapq.heappush(
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queue,
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(
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(heuristic(n_row, n_col) + length + 1, length + 1),
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(n_row, n_col),
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),
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)
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if end not in visited:
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return None
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path: list[tuple[int, int]] = [end]
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while path[-1] != start:
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path.append(parents[path[-1]])
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return list(reversed(path))
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def print_path(path: list[tuple[int, int]], n_rows: int, n_cols: int) -> None:
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_, end = path[0], path[-1]
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graph = [["." for _c in range(n_cols)] for _r in range(n_rows)]
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graph[end[0]][end[1]] = "E"
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for i in range(0, len(path) - 1):
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cr, cc = path[i]
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nr, nc = path[i + 1]
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if cr == nr and nc == cc - 1:
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graph[cr][cc] = "<"
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elif cr == nr and nc == cc + 1:
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graph[cr][cc] = ">"
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elif cr == nr - 1 and nc == cc:
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graph[cr][cc] = "v"
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elif cr == nr + 1 and nc == cc:
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graph[cr][cc] = "^"
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else:
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assert False, "{} -> {} infeasible".format(path[i], path[i + 1])
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print("\n".join("".join(row) for row in graph))
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lines = sys.stdin.read().splitlines()
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grid = [[ord(cell) - ord("a") for cell in line] for line in lines]
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start: tuple[int, int]
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end: tuple[int, int]
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# for part 2
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start_s: list[tuple[int, int]] = []
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for i_row, row in enumerate(grid):
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for i_col, col in enumerate(row):
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if chr(col + ord("a")) == "S":
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start = (i_row, i_col)
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start_s.append(start)
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elif chr(col + ord("a")) == "E":
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end = (i_row, i_col)
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elif col == 0:
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start_s.append((i_row, i_col))
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# fix values
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grid[start[0]][start[1]] = 0
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grid[end[0]][end[1]] = ord("z") - ord("a")
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path = dijkstra(start, end, grid)
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assert path is not None
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print_path(path, n_rows=len(grid), n_cols=len(grid[0]))
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answer_1 = len(path) - 1
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print(f"answer 1 is {answer_1}")
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answer_2 = min(
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len(path) - 1
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for start in start_s
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if (path := dijkstra(start, end, grid)) is not None
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)
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print(f"answer 2 is {answer_2}")
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