this post was submitted on 05 Dec 2025
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Advent Of Code

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An unofficial home for the advent of code community on programming.dev! Other challenges are also welcome!

Advent of Code is an annual Advent calendar of small programming puzzles for a variety of skill sets and skill levels that can be solved in any programming language you like.

Everybody Codes is another collection of programming puzzles with seasonal events.

EC 2025

AoC 2025

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๐ŸŽ„ - 2025 DAY 5 SOLUTIONS - ๐ŸŽ„ (programming.dev)
submitted 2 weeks ago by CameronDev@programming.dev to c/advent_of_code@programming.dev
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Day 5: Cafeteria

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[โ€“] EnEnCode@programming.dev 2 points 2 weeks ago

Well, I guess I've decided to do AoC this year. Trivial problem, though I shamelessly stole some range-merging code from AoC 2022 (it was when I was still well in the learning phase of Rust). If you can't look at old code and wonder WTF you were thinking, have you really gotten any better?

Solution (mostly uninteresting)

pub fn day05(input: &str) -> (u64, u64) {
    let mut part1 = 0;
    let mut part2 = 0;
    let mut ranges = Vec::new();
    let mut lines = input.trim().lines();
    for line in lines.by_ref() {
        if line.is_empty() {
            break;
        }
        let range = line
            .split_once('-')
            .map(|(l, h)| [l.parse::<u64>().unwrap(), h.parse::<u64>().unwrap()])
            .unwrap();
        ranges.push(range);
    }
    let ranges = combine_ranges(ranges);
    for idx in lines {
        for r in ranges.iter() {
            if (r[0]..=r[1]).contains(&idx.parse::<u64>().unwrap()) {
                part1 += 1;
                break;
            }
        }
    }
    for r in ranges {
        part2 += r[1] - r[0] + 1;
    }
    (part1, part2)
}

combine_ranges WARNING : Hideous, triggers Clippy, not blazingly fast

fn combine_ranges(ranges: Vec<[u64; 2]>) -> Vec<[u64; 2]> {
    let mut temp_ranges = ranges;
    let mut comp_ranges: Vec<[u64; 2]> = Vec::new();
    let mut run_again: bool = true;
    while run_again {
        run_again = false;
        comp_ranges = Vec::new();
        'outer: for i in 0..temp_ranges.len() {
            for j in 0..comp_ranges.len() {
                if temp_ranges[i][0] <= comp_ranges[j][0] && comp_ranges[j][1] <= temp_ranges[i][1]
                {
                    //temp covers all of comp
                    comp_ranges[j][0] = temp_ranges[i][0];
                    comp_ranges[j][1] = temp_ranges[i][1];
                    run_again = true;
                    continue 'outer;
                } else if comp_ranges[j][0] <= temp_ranges[i][0]
                    && temp_ranges[i][1] <= comp_ranges[j][1]
                {
                    //comp covers all of temp
                    run_again = true;
                    continue 'outer;
                } else if temp_ranges[i][0] <= comp_ranges[j][0]
                    && comp_ranges[j][0] <= temp_ranges[i][1]
                    && temp_ranges[i][1] <= comp_ranges[j][1]
                {
                    //grow left
                    comp_ranges[j][0] = temp_ranges[i][0];
                    run_again = true;
                    continue 'outer;
                } else if comp_ranges[j][0] <= temp_ranges[i][0]
                    && temp_ranges[i][0] <= comp_ranges[j][1]
                    && comp_ranges[j][1] <= temp_ranges[i][1]
                {
                    //grow right
                    comp_ranges[j][1] = temp_ranges[i][1];
                    run_again = true;
                    continue 'outer;
                }
            }
            comp_ranges.push(temp_ranges[i]);
        }
        temp_ranges = comp_ranges.clone();
    }

    comp_ranges
}