mirror of
https://github.com/Threnklyn/advent-of-code-go.git
synced 2026-05-18 19:13:27 +02:00
alexchao26
100 lines
3.1 KiB
Python
100 lines
3.1 KiB
Python
def part1(input: str) -> int:
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grid: list[list[int, int]] = []
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for line in input.splitlines():
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grid.append([int(x) for x in list(line)])
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# alternative pythonic way...
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# grid = [[int(char) for char in line] for line in input.splitlines()]
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ans: int = 0
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for r in range(len(grid)):
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for c in range(len(grid[0])):
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if grid[r][c] == 0:
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ans += len(dfs_backtrack_unique_end_coords(grid, r, c, {(r, c)}))
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return ans
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# I misread the instructions slightly and went for a "unique paths" algo at first.
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# It would be simpler to pass the "reachable 9s coords" set in as an arg and update
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# it in the termination case, then take the length of that set in the part1() function.
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# This would remove the need to combine the sets which is potentially expensive (and ugly)
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def dfs_backtrack_unique_end_coords(
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grid: list[list[int, int]], row: int, col: int, visited: set[tuple[int, int]]
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) -> set[tuple[int, int]]:
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if grid[row][col] == 9:
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return {(row, col)}
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all_coords: set[tuple[int, int]] = set()
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for diff in [(-1, 0), (1, 0), (0, -1), (0, 1)]:
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nextRow = row + diff[0]
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nextCol = col + diff[1]
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if not (0 <= nextRow < len(grid) and 0 <= nextCol < len(grid[0])):
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continue
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if (nextRow, nextCol) in visited:
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continue
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if grid[nextRow][nextCol] == grid[row][col] + 1:
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visited.add((nextRow, nextCol))
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new_coords = dfs_backtrack_unique_end_coords(
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grid, nextRow, nextCol, visited
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)
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# combines the two sets, see comment above function def
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all_coords.update(new_coords)
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visited.remove((nextRow, nextCol))
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return all_coords
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def part2(input: str) -> int:
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grid = [[int(char) for char in line] for line in input.splitlines()]
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ans: int = 0
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for r in range(len(grid)):
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for c in range(len(grid[0])):
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if grid[r][c] == 0:
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ans += dfs_backtrack_unique_paths(grid, r, c, {(r, c)})
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return ans
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def dfs_backtrack_unique_paths(
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grid: list[list[int, int]], row: int, col: int, visited: set[tuple[int, int]]
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) -> int:
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if grid[row][col] == 9:
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# unique path found
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return 1
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total: int = 0
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for diff in [(-1, 0), (1, 0), (0, -1), (0, 1)]:
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nextRow = row + diff[0]
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nextCol = col + diff[1]
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if not (0 <= nextRow < len(grid) and 0 <= nextCol < len(grid[0])):
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continue
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if (nextRow, nextCol) in visited:
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continue
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if grid[nextRow][nextCol] == grid[row][col] + 1:
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visited.add((nextRow, nextCol))
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total += dfs_backtrack_unique_paths(grid, nextRow, nextCol, visited)
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visited.remove((nextRow, nextCol))
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return total
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example = """89010123
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78121874
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87430965
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96549874
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45678903
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32019012
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01329801
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10456732"""
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input = open("input.txt").read().strip()
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print(f"part1 example: {part1(example)} want 36")
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print(f"part1: {part1(input)} want 782")
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print(f"part2 example: {part2(example)} want 81")
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print(f"part2 example: {part2(input)} want 1694")
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