mirror of
https://github.com/Threnklyn/advent-of-code-go.git
synced 2026-05-18 19:13:27 +02:00
alexchao26
113 lines
3.2 KiB
Python
113 lines
3.2 KiB
Python
def part1(input: str, grid_size: int, fallen_bytes: int) -> int:
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# simulate fallen_bytes
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# path find from top left to bottom right
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grid = [["." for _ in range(grid_size)] for _ in range(grid_size)]
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for line in input.splitlines()[:fallen_bytes]:
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parts = line.split(",")
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col = int(parts[0])
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row = int(parts[1])
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grid[row][col] = "#"
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queue: list[tuple[int, int, int]] = [(0, 0, 0)]
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visited: set[tuple[int, int]] = set()
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while len(queue) > 0:
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front = queue.pop(0)
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if front[:2] in visited:
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continue
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visited.add(front[:2])
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if front[0] == grid_size - 1 and front[1] == grid_size - 1:
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return front[2]
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for diff in [(0, 1), (1, 0), (0, -1), (-1, 0)]:
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next_row = front[0] + diff[0]
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next_col = front[1] + diff[1]
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if 0 <= next_row < grid_size and 0 <= next_col < grid_size:
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if grid[next_row][next_col] != "#":
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queue.append((next_row, next_col, front[2] + 1))
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raise Exception("should return from loop")
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def part2(input: str, grid_size: int) -> str:
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grid = [["." for _ in range(grid_size)] for _ in range(grid_size)]
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# drop all fallen bytes, then remove them selectively and attempt to continue
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# path finding from there?
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fallen_bytes: list[tuple[int, int]] = []
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for line in input.splitlines():
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parts = line.split(",")
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col = int(parts[0])
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row = int(parts[1])
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grid[row][col] = "#"
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fallen_bytes.append((row, col))
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# get set of all reachable coords from the starting point
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reachable: set[tuple[int, int]] = {(0, 0)}
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flood_fill_from(grid, (0, 0), reachable)
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# iterate in reverse through fallen bytes and if the byte is adjacent to a reachable
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# cell, then try to flood fill from the adjacent cell's neighbors
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for fallen in reversed(fallen_bytes):
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grid[fallen[0]][fallen[1]] = "."
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for diff in [(0, 1), (1, 0), (0, -1), (-1, 0)]:
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next = (fallen[0] + diff[0], fallen[1] + diff[1])
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if next in reachable:
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if flood_fill_from(grid, next, reachable):
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return f"{fallen[1]},{fallen[0]}"
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raise Exception("should return from loop")
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def flood_fill_from(
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grid: list[list[str]], coord: tuple[int, int], reachable: set[tuple[int, int]]
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) -> bool:
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for diff in [(0, 1), (1, 0), (0, -1), (-1, 0)]:
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next_row = coord[0] + diff[0]
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next_col = coord[1] + diff[1]
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if (next_row, next_col) not in reachable:
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if 0 <= next_row < len(grid) and 0 <= next_col < len(grid):
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if grid[next_row][next_col] != "#":
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reachable.add((next_row, next_col))
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flood_fill_from(grid, (next_row, next_col), reachable)
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return (len(grid) - 1, len(grid) - 1) in reachable
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# col, row (x, y)
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example = """5,4
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4,2
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4,5
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3,0
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2,1
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6,3
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2,4
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1,5
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0,6
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3,3
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2,6
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5,1
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1,2
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5,5
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2,5
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6,5
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1,4
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0,4
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6,4
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1,1
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6,1
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1,0
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0,5
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1,6
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2,0"""
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input = open("input.txt").read().strip()
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print(f"part1 example: {part1(example, 6 + 1, 12)} want 22")
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print(f"part1 actual: {part1(input, 70 + 1, 1024)} want 298")
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print(f"part2 example: {part2(example, 6 + 1)} want '6,1'")
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print(f"part2 actual: {part2(input, 70 + 1)} want 52,32")
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