adventofcode2023/day05-2.py

from helpers import Helper

helper = Helper(debug=True)
load_input = helper.load_input
debug = helper.debug

# FUTURE ME: HERE'S THE KEY
# You don't have to check every seed.
# Instead, create ranges, and use the later steps to cut those ranges
# into chunks. The smallest value in the smallest chunk after the last
# step is the solution. The brute-force solution takes an enormous amount
# of time; the chunk solution is still polynomial time, I think, but 
# the n is much smaller (dozens rather than hundreds of millions).

def within(target, start, end):
    if start == end:
        return target == start
    if start > end:
        start, end = end, start
    return target >= start and end >= target

def chunk_it(old_range, new_range):
    o_start, o_end = old_range
    n_start, n_end = new_range
    debug(o_start, o_end, n_start, n_end)

    # The new range is entirely outside the current range
    if n_end < o_start or n_start > o_end:
        debug("Entirely outside!")
        return sorted([old_range, new_range], key=lambda n:n[0])
    
    # The new range is entirely within the current range
    if n_start >= o_start and n_end <= o_end:
        # We've already accounted for this range
        debug("Already got it")
        return [old_range]

    # The new range starts lower and ends higher
    if n_start <= o_start and n_end >= o_end:
        # We can replace the old range with the new one
        debug("Replacement!")
        return [new_range]

    # The new range starts lower but ends within
    if n_start <= o_start and n_end >= o_start and n_end <= o_end:
        debug("Starts before")
        return [[n_start, o_end]]

    # The new range starts within but ends higher
    if n_end >= o_end and n_start >= o_start and n_start <= o_end:
        debug("Ends after")
        return [[o_start, n_end]]
    
    raise Exception(f"What? What? Nothing matched: {old_range}, {new_range}")

def main():
    lines = load_input(5)

    maps_dict = {
        "seeds": [],
        "seed-to-soil": [],
        "soil-to-fertilizer": [],
        "fertilizer-to-water": [],
        "water-to-light": [],
        "light-to-temperature": [],
        "temperature-to-humidity": [],
        "humidity-to-location": [],
    }
    maps_keys = list(maps_dict.keys())
    maps_dict["seeds"] = [int(n) for n in lines[0].split()[1:]]
    debug(f"Starting with {len(maps_dict['seeds'])//2} ranges")
    real_seeds = []
    i, j = 0, 1
    while j < len(maps_dict["seeds"]):
        new_range = [maps_dict["seeds"][i], maps_dict["seeds"][i] + maps_dict["seeds"][j]]
        if len(real_seeds) == 0:
            real_seeds.append(new_range)
        else:
            new_real_seeds = []
            for range in real_seeds:
                add_ranges = chunk_it(range, new_range)
                debug(add_ranges)
                for r in add_ranges:
                    if r not in new_real_seeds:
                        new_real_seeds.append(r)
            real_seeds = list(new_real_seeds)
        i += 2
        j += 2
        debug(real_seeds, i, j)
    debug(f"Found {len(real_seeds)} actual ranges")
    real_seeds.sort(key=lambda n: n[0])
    # debug(real_seeds)
    return
        # new_start = maps_dict["seeds"][i]
        # new_end = new_start + maps_dict["seeds"][j]
        # debug(f"Adding seeds in range {new_start}-{new_end}")
        # new_seeds = range(new_start, new_end)
        # debug(new_seeds)
        # real_seeds.append(new_seeds)
        # debug(real_seeds)
    seeds_list = [{"seed": seed[1]} for seed in real_seeds]
    
    current_key = ""
    for line in lines[1:]:
        if line == "":
            continue
        split_line = line.split()
        if split_line[0] in maps_keys:
            current_key = split_line[0]
        else:
            maps_dict[current_key].append({
                x: int(a)
                for (x, a) 
                in zip(["destination", "source", "length"], split_line)}
                )
    for seed in seeds_list:
        for key in maps_keys[1:]:
            source, _, destination = key.split("-")
            i = 0
            t_list = maps_dict[key]
            while i < len(t_list):
                s_map = t_list[i]
                # debug(f"Checking {seed[source]} against {s_map['source']}, {s_map['source'] + s_map['length']}")
                if within(seed[source], s_map["source"], (s_map["source"] + s_map["length"])):
                    
                    source_distance = seed[source] - s_map["source"]
                    seed[destination] = s_map["destination"] + source_distance
                    # debug("{}: {} found in {}+{}, {} is {} + {}".format(
                    #     source,
                    #     seed[source],
                    #     s_map["source"],
                    #     s_map["length"],
                    #     seed[destination],
                    #     s_map["destination"],
                    #     source_distance
                    # ))
                    i = len(t_list)
                else:
                    # debug("{}: {} not found in {}+{}, using original".format(
                    #     source,
                    #     seed[source],
                    #     s_map["source"],
                    #     s_map["length"]
                    # ))
                    i += 1
            if not seed.get(destination, None):
                seed[destination] = seed[source]
    debug("\n".join([f"{k}: {v}" for k, v in seed.items() for seed in seeds_list]))
    print(min(seeds_list, key=lambda x: x["location"]))

if __name__ == "__main__":
    main()