adventofcode2023/day5/src/main.rs

use std::fs::read_to_string;
use std::cmp;
use std::time::Instant;

fn get_numbers_in_line(str: &str) -> Vec<u32> {
    return str.split_whitespace().filter_map(|substr| substr.parse::<u32>().ok()).collect();
}

fn process(seeds: Vec<u32>, mut maps: Vec<Vec<(u32, u32, u32)>>) -> (u32, u32) {
    for map in maps.iter_mut() {
        map.sort_unstable_by(|&(a, _, _), &(b, _, _)| a.partial_cmp(&b).unwrap());
    }
    // Task 1 - mapping a single number through all mappings
    let min1 = seeds.iter().map(
        |seed| {
            let mut n = *seed;
            for map in &maps {
                for &(src, dst, len) in map {
                    if src > n {
                        break;
                    }
                    if n - src < len {
                        n = n - src + dst;
                        break;
                    }
                }
            }
            n
        }
    ).min().unwrap();

    // Task 2 - mapping whole ranges through all mappings
    // Array of ranges that will be mapped for task 2 initialized with pairs from seeds
    let mut processed_ranges: Vec<_> = (0..seeds.len()).step_by(2).map(|i| (seeds[i], seeds[i + 1])).collect();
    let mut swap_ranges: Vec<(u32, u32)> = Vec::new();
    // Map the processed_ranged through all mappings
    for map in &maps {
        swap_ranges.clear();
        for &(working_start, working_len) in &processed_ranges {
            // Applying one or more mapping ranges to the processed range
            let (mut temp_start, mut temp_len) = (working_start, working_len);
            for &(src, dst, len) in map {
                // Working range starts before mapping range, means it's an unmapped segment
                if temp_start < src {
                    let out_len = cmp::min(temp_len, src - temp_start);
                    swap_ranges.push((temp_start, out_len));
                    if out_len == temp_len {
                        break;
                    }
                    temp_start = src;
                }
                // Working range is sure to not begin before mapping range
                let start_diff = temp_start - src;
                // Mapping range is so short that it doesn't reach the working range, skip
                if len <= start_diff {
                    continue;
                }
                let out_len = cmp::min(temp_len, len - start_diff);
                swap_ranges.push((dst + start_diff, out_len));
                if out_len == temp_len {
                    break;
                }
                // Consume the beginning of the working range
                temp_start += out_len;
                temp_len -= out_len;
            }
        }
        std::mem::swap(&mut processed_ranges, &mut swap_ranges);
    }
    // Find the range with lowest starting value, length is guaranteed to be nonzero
    let min2 = processed_ranges.iter().map(|&(start, _)| start).min().unwrap();
    (min1, min2)
}

fn main() {
    let time_start = Instant::now();
    // Set of inputs
    let mut seeds: Vec<u32> = Vec::new();
    // Mappings of ranges, ordered in order to easily find the lowest relevant range
    // Order: (src, dst, len)
    let mut maps: Vec<Vec<(u32, u32, u32)>> = Vec::new();
    maps.push(Vec::new());
    let mut did_read_seeds: bool = false;
    for line in read_to_string("input.txt").unwrap().lines() {
        if !did_read_seeds {
            seeds = get_numbers_in_line(line);
            did_read_seeds = true;
        } else {
            let numbers = get_numbers_in_line(line);
            if numbers.len() == 3 {
                maps.last_mut().unwrap().push((numbers[1],numbers[0], numbers[2]));
            } else {
                if !maps.last().unwrap().is_empty() {
                    maps.push(Vec::new());
                }
            }
        }
    }
    if maps.last().unwrap().is_empty() {
        maps.pop();
    }
    let time_start_no_io = Instant::now();

    // for _ in 0..1000 {
    //    let (_, _) = process(seeds.clone(), maps.clone());
    // }
    let (min1, min2) = process(seeds, maps);

    // Measurements
    let elapsed = time_start.elapsed().as_nanos();
    let elapsed_no_io = time_start_no_io.elapsed().as_nanos();
    println!("Time: {}ns", elapsed);
    println!("Time without file i/o: {}ns", elapsed_no_io);
    println!("Min location1: {}", min1);
    println!("Min location2: {}", min2);
}