--- 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.
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
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
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:
99. The destination range is the same length, but it starts at
50, so its two values are
51. With this information, you know that seed number
98 corresponds to soil number
50 and that seed number
99 corresponds to soil number
The second line means that the source range starts at
50 and contains
97. This corresponds to a destination range starting at
52 and also containing
99. So, seed number
53 corresponds to soil number
Any source numbers that aren't mapped correspond to the same destination number. So, seed number
10 corresponds to soil number
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
79corresponds to soil number
- Seed number
14corresponds to soil number
- Seed number
55corresponds to soil number
- Seed number
13corresponds to soil number
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:
So, the lowest location number in this example is
What is the lowest location number that corresponds to any of the initial seed numbers?