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Solution to problem 5 in Python

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David Doblas Jiménez 2023-12-06 09:36:36 +01:00
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# --- Day 5: If You Give A Seed A Fertilizer ---
# You take the boat and find the gardener right where you were told he would be:
# managing a giant "garden" that looks more to you like a farm.
# "A water source? Island Island is the water source!" You point out that Snow
# Island isn't receiving any water.
# "Oh, we had to stop the water because we ran out of sand to filter it with!
# Can't make snow with dirty water. Don't worry, I'm sure we'll get more sand
# soon; we only turned off the water a few days... weeks... oh no." His face
# sinks into a look of horrified realization.
# "I've been so busy making sure everyone here has food that I completely forgot
# to check why we stopped getting more sand! There's a ferry leaving soon that
# is headed over in that direction - it's much faster than your boat. Could you
# please go check it out?"
# You barely have time to agree to this request when he brings up another.
# "While you wait for the ferry, maybe you can help us with our food production
# problem. The latest Island Island Almanac just arrived and we're having
# trouble making sense of it."
# The almanac (your puzzle input) lists all of the seeds that need to be
# planted. It also lists what type of soil to use with each kind of seed, what
# type of fertilizer to use with each kind of soil, what type of water to use
# with each kind of fertilizer, and so on. Every type of seed, soil, fertilizer
# and so on is identified with a number, but numbers are reused by each category
# - that is, soil 123 and fertilizer 123 aren't necessarily related to each
# other.
# For example:
# seeds: 79 14 55 13
# seed-to-soil map:
# 50 98 2
# 52 50 48
# soil-to-fertilizer map:
# 0 15 37
# 37 52 2
# 39 0 15
# fertilizer-to-water map:
# 49 53 8
# 0 11 42
# 42 0 7
# 57 7 4
# water-to-light map:
# 88 18 7
# 18 25 70
# light-to-temperature map:
# 45 77 23
# 81 45 19
# 68 64 13
# temperature-to-humidity map:
# 0 69 1
# 1 0 69
# humidity-to-location map:
# 60 56 37
# 56 93 4
# The almanac starts by listing which seeds need to be planted: seeds 79, 14,
# 55, and 13.
# The rest of the almanac contains a list of maps which describe how to convert
# numbers from a source category into numbers in a destination category. That
# is, the section that starts with seed-to-soil map: describes how to convert a
# seed number (the source) to a soil number (the destination). This lets the
# gardener and his team know which soil to use with which seeds, which water to
# use with which fertilizer, and so on.
# Rather than list every source number and its corresponding destination number
# one by one, the maps describe entire ranges of numbers that can be converted.
# Each line within a map contains three numbers: the destination range start,
# the source range start, and the range length.
# Consider again the example seed-to-soil map:
# 50 98 2
# 52 50 48
# The first line has a destination range start of 50, a source range start of
# 98, and a range length of 2. This line means that the source range starts at
# 98 and contains two values: 98 and 99. The destination range is the same
# length, but it starts at 50, so its two values are 50 and 51. With this
# information, you know that seed number 98 corresponds to soil number 50 and
# that seed number 99 corresponds to soil number 51.
# The second line means that the source range starts at 50 and contains 48
# values: 50, 51, ..., 96, 97. This corresponds to a destination range starting
# at 52 and also containing 48 values: 52, 53, ..., 98, 99. So, seed number 53
# corresponds to soil number 55.
# Any source numbers that aren't mapped correspond to the same destination
# number. So, seed number 10 corresponds to soil number 10.
# So, the entire list of seed numbers and their corresponding soil numbers looks
# like this:
# seed soil
# 0 0
# 1 1
# ... ...
# 48 48
# 49 49
# 50 52
# 51 53
# ... ...
# 96 98
# 97 99
# 98 50
# 99 51
# With this map, you can look up the soil number required for each initial seed
# number:
# Seed number 79 corresponds to soil number 81.
# Seed number 14 corresponds to soil number 14.
# Seed number 55 corresponds to soil number 57.
# Seed number 13 corresponds to soil number 13.
# The gardener and his team want to get started as soon as possible, so they'd
# like to know the closest location that needs a seed. Using these maps, find
# the lowest location number that corresponds to any of the initial seeds. To do
# this, you'll need to convert each seed number through other categories until
# you can find its corresponding location number. In this example, the
# corresponding types are:
# Seed 79, soil 81, fertilizer 81, water 81, light 74, temperature 78,
# humidity 78, location 82.
# Seed 14, soil 14, fertilizer 53, water 49, light 42, temperature 42,
# humidity 43, location 43.
# Seed 55, soil 57, fertilizer 57, water 53, light 46, temperature 82,
# humidity 82, location 86.
# Seed 13, soil 13, fertilizer 52, water 41, light 34, temperature 34,
# humidity 35, location 35.
# So, the lowest location number in this example is 35.
# What is the lowest location number that corresponds to any of the initial seed
# numbers?
with open("files/P5.txt") as f:
almanac = [line for line in f.read().strip().split("\n\n")]
seed, *maps = almanac
seeds = [int(s) for s in seed.split(":")[1].split()]
mappings = [
[[int(i) for i in line.split()] for line in m.splitlines()[1:]]
for m in maps
]
def part1():
locations = seeds
for mapping in mappings:
new_locations = []
for location in locations:
new_val = location
for destination, start, size in mapping:
if start <= location < start + size:
new_val = location - start + destination
break
new_locations.append(new_val)
locations = new_locations
print(f"The lowest location is {min(locations)}")
# --- Part Two ---
# Everyone will starve if you only plant such a small number of seeds.
# Re-reading the almanac, it looks like the seeds: line actually describes
# ranges of seed numbers.
# The values on the initial seeds: line come in pairs. Within each pair, the
# first value is the start of the range and the second value is the length of
# the range. So, in the first line of the example above:
# seeds: 79 14 55 13
# This line describes two ranges of seed numbers to be planted in the garden.
# The first range starts with seed number 79 and contains 14 values: 79, 80,
# ..., 91, 92. The second range starts with seed number 55 and contains 13
# values: 55, 56, ..., 66, 67.
# Now, rather than considering four seed numbers, you need to consider a total
# of 27 seed numbers.
# In the above example, the lowest location number can be obtained from seed
# number 82, which corresponds to soil 84, fertilizer 84, water 84, light 77,
# temperature 45, humidity 46, and location 46. So, the lowest location number
# is 46.
# Consider all of the initial seed numbers listed in the ranges on the first
# line of the almanac. What is the lowest location number that corresponds to
# any of the initial seed numbers?
def get_ranges(span_start, span_end, map_start, map_end):
if span_start < map_start and map_end < span_end:
return [(map_start, map_end)], [
(span_start, map_start - 1),
(map_end + 1, span_end),
]
elif map_start <= span_start and span_end <= map_end:
return [(span_start, span_end)], []
elif span_start < map_start <= span_end:
return [(map_start, span_end)], [(span_start, map_start - 1)]
elif span_start <= map_end < span_end:
return [(span_start, map_end)], [(map_end + 1, span_end)]
else:
return [], [(span_start, span_end)]
new_mappings = [
[
[destination - start, start, start + size - 1]
for destination, start, size in m
]
for m in mappings
]
def part2():
ranges = [
(seeds[i], seeds[i] + seeds[i + 1] - 1)
for i in range(0, len(seeds), 2)
]
for mapping in new_mappings:
new_ranges = []
for seed_span in ranges:
unprocessed = [seed_span]
for offset, map_start, map_end in mapping:
new_unprocessed = []
for span_start, span_end in unprocessed:
map1, map2 = get_ranges(
span_start, span_end, map_start, map_end
)
new_unprocessed += map2
new_ranges += [(a + offset, b + offset) for a, b in map1]
unprocessed = new_unprocessed
new_ranges += unprocessed
ranges = new_ranges
print(f"The lowest location is {min(idx for idx, _ in ranges)}")
if __name__ == "__main__":
part1()
part2()