130 lines
4.0 KiB
Python
130 lines
4.0 KiB
Python
import sys
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from typing import Sequence
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MAP_ORDER = [
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"seed",
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"soil",
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"fertilizer",
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"water",
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"light",
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"temperature",
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"humidity",
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"location",
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]
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lines = sys.stdin.read().splitlines()
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# mappings from one category to another, each list contains
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# ranges stored as (source, target, length), ordered by start and
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# completed to have no "hole"
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maps: dict[tuple[str, str], list[tuple[int, int, int]]] = {}
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# parsing
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index = 2
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while index < len(lines):
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p1, _, p2 = lines[index].split()[0].split("-")
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# extract the existing ranges from the file - we store as (source, target, length)
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# whereas the file is in order (target, source, length)
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index += 1
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values: list[tuple[int, int, int]] = []
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while index < len(lines) and lines[index]:
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n1, n2, n3 = lines[index].split()
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values.append((int(n2), int(n1), int(n3)))
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index += 1
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# sort by source value
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values.sort()
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# add a 'fake' interval starting at 0 if missing
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if values[0][0] != 0:
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values.insert(0, (0, 0, values[0][0]))
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# fill gaps between intervals
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for i in range(len(values) - 1):
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next_start = values[i + 1][0]
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end = values[i][0] + values[i][2]
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if next_start != end:
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values.insert(
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i + 1,
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(end, end, next_start - end),
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)
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# add an interval covering values up to at least 2**32 at the end
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last_start, _, last_length = values[-1]
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values.append((last_start + last_length, last_start + last_length, 2**32))
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assert all(v1[0] + v1[2] == v2[0] for v1, v2 in zip(values[:-1], values[1:]))
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assert values[0][0] == 0
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assert values[-1][0] + values[-1][-1] >= 2**32
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maps[p1, p2] = values
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index += 1
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def find_range(
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values: tuple[int, int], map: list[tuple[int, int, int]]
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) -> list[tuple[int, int]]:
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"""
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Given an input range, use the given mapping to find the corresponding list of
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ranges in the target domain.
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"""
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r_start, r_length = values
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ranges: list[tuple[int, int]] = []
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# find index of the first and last intervals in map that overlaps the input
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# interval
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index_start, index_end = -1, -1
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for index_start, (start, _, length) in enumerate(map):
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if start <= r_start and start + length > r_start:
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break
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for index_end, (start, _, length) in enumerate(
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map[index_start:], start=index_start
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):
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if r_start + r_length >= start and r_start + r_length < start + length:
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break
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assert index_start >= 0 and index_end >= 0
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# special case if one interval contains everything
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if index_start == index_end:
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start, target, length = map[index_start]
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ranges.append((target + r_start - start, r_length))
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else:
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# add the start interval part
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start, target, length = map[index_start]
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ranges.append((target + r_start - start, start + length - r_start))
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# add all intervals between the first and last (excluding both)
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index = index_start + 1
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while index < index_end:
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start, target, length = map[index]
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ranges.append((target, length))
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index += 1
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# add the last interval
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start, target, length = map[index_end]
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ranges.append((target, r_start + r_length - start))
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return ranges
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def find_location_ranges(seeds: Sequence[tuple[int, int]]) -> Sequence[tuple[int, int]]:
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for map1, map2 in zip(MAP_ORDER[:-1], MAP_ORDER[1:]):
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seeds = [s2 for s1 in seeds for s2 in find_range(s1, maps[map1, map2])]
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return seeds
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# part 1 - use find_range() with range of length 1
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seeds_p1 = [(int(s), 1) for s in lines[0].split(":")[1].strip().split()]
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answer_1 = min(start for start, _ in find_location_ranges(seeds_p1))
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print(f"answer 1 is {answer_1}")
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# # part 2
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parts = lines[0].split(":")[1].strip().split()
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seeds_p2 = [(int(s), int(e)) for s, e in zip(parts[::2], parts[1::2])]
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answer_2 = min(start for start, _ in find_location_ranges(seeds_p2))
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print(f"answer 2 is {answer_2}")
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