Nim

I hope y’all like nested loops:

• Day 3, part 1
• Day 3, part 2

That was not fun to solve. Lots of ugly code. This is a less ugly second version. Language: Nim.

day_03.nim

I wrote today’s program in Python. (I am going to do a different language each day.) The only thing that gave me a little trouble was I was counting “\n” as a part label. Once I realized that I was able to get both problems done very quickly.

My code for the two parts is on github:-

• https://github.com/pngwen/advent-2023/blob/main/day-3a.py
• https://github.com/pngwen/advent-2023/blob/main/day-3b.py

Rust

I’ve been using Regexes for every day so far, this time it helped in finding numbers along with their start and end position in a line. For the second part I mostly went with the approach of part 1 which was to look at all numbers and then figure out if it has a part symbol around it. Only in part 2 I saved all numbers next to a gear * in a hash table that maps each gear position to a list of adjacent numbers. Then in the end I can just look at all gears with exactly 2 numbers attached.

Also it has to be said, multiplying two numbers is the exact opposite of getting their ratio!

Edit: Updated now with part 2.

Managed to have a crack at this a bit earlier today, I’ve only done Part 01 so far. I’ll update with Part 02 later.

I tackled this with the personal challenge of not loading the entire puzzle input into memory, which would have made this a bit easier.

Solution in Rust 🦀

View formatted on GitLab

use std::{
    env, fs,
    io::{self, BufRead, BufReader, Read},
};

fn main() -> io::Result<()> {
    let args: Vec = env::args().collect();
    let filename = &args[1];
    let file1 = fs::File::open(filename)?;
    let file2 = fs::File::open(filename)?;
    let reader1 = BufReader::new(file1);
    let reader2 = BufReader::new(file2);

    println!("Part one: {}", process_part_one(reader1));
    println!("Part two: {}", process_part_two(reader2));
    Ok(())
}

fn process_part_one(reader: BufReader) -> u32 {
    let mut lines = reader.lines().peekable();
    let mut prev_line: Option = None;
    let mut sum = 0;
    while let Some(line) = lines.next() {
        let current_line = line.expect("line exists");
        let next_line = match lines.peek() {
            Some(Ok(line)) => Some(line),
            Some(Err(_)) => None,
            None => None,
        };
        match (prev_line, next_line) {
            (None, Some(next)) => {
                let lines = vec![¤t_line, next];
                sum += parse_lines(lines, true);
            }
            (Some(prev), Some(next)) => {
                let lines = vec![&prev, ¤t_line, next];
                sum += parse_lines(lines, false);
            }
            (Some(prev), None) => {
                let lines = vec![&prev, ¤t_line];
                sum += parse_lines(lines, false);
            }
            (None, None) => {}
        }

        prev_line = Some(current_line);
    }
    sum
}

fn process_part_two(reader: BufReader) -> u32 {
    let mut lines = reader.lines().peekable();
    let mut prev_line: Option = None;
    let mut sum = 0;
    while let Some(line) = lines.next() {
        let current_line = line.expect("line exists");
        let next_line = match lines.peek() {
            Some(Ok(line)) => Some(line),
            Some(Err(_)) => None,
            None => None,
        };
        match (prev_line, next_line) {
            (None, Some(next)) => {
                let lines = vec![¤t_line, next];
                sum += parse_lines_for_gears(lines, true);
            }
            (Some(prev), Some(next)) => {
                let lines = vec![&prev, ¤t_line, next];
                sum += parse_lines_for_gears(lines, false);
            }
            (Some(prev), None) => {
                let lines = vec![&prev, ¤t_line];
                sum += parse_lines_for_gears(lines, false);
            }
            (None, None) => {}
        }

        prev_line = Some(current_line);
    }

    sum
}

fn parse_lines(lines: Vec<&String>, first_line: bool) -> u32 {
    let mut sum = 0;
    let mut num = 0;
    let mut valid = false;
    let mut char_vec: Vec> = Vec::new();
    for line in lines {
        char_vec.push(line.chars().collect());
    }
    let chars = match first_line {
        true => &char_vec[0],
        false => &char_vec[1],
    };
    for i in 0..chars.len() {
        if chars[i].is_digit(10) {
            // Add the digit to the number
            num = num * 10 + chars[i].to_digit(10).expect("is digit");

            // Check the surrounding character for non-period symbols
            for &x in &[-1, 0, 1] {
                for chars in &char_vec {
                    if (i as isize + x).is_positive() && ((i as isize + x) as usize) < chars.len() {
                        let index = (i as isize + x) as usize;
                        if !chars[index].is_digit(10) && chars[index] != '.' {
                            valid = true;
                        }
                    }
                }
            }
        } else {
            if valid {
                sum += num;
            }
            valid = false;
            num = 0;
        }
    }
    if valid {
        sum += num;
    }
    sum
}

fn parse_lines_for_gears(lines: Vec<&String>, first_line: bool) -> u32 {
    let mut sum = 0;
    let mut char_vec: Vec> = Vec::new();
    for line in &lines {
        char_vec.push(line.chars().collect());
    }
    let chars = match first_line {
        true => &char_vec[0],
        false => &char_vec[1],
    };
    for i in 0..chars.len() {
        if chars[i] == '*' {
            let surrounding_nums = get_surrounding_numbers(&lines, i);
            let product = match surrounding_nums.len() {
                0 | 1 => 0,
                _ => surrounding_nums.iter().product(),
            };
            sum += product;
        }
    }
    sum
}

fn get_surrounding_numbers(lines: &Vec<&String>, gear_pos: usize) -> Vec {
    let mut nums: Vec = Vec::new();
    let mut num: u32 = 0;
    let mut valid = false;
    for line in lines {
        for (i, char) in line.chars().enumerate() {
            if char.is_digit(10) {
                num = num * 10 + char.to_digit(10).expect("is digit");
                if [gear_pos - 1, gear_pos, gear_pos + 1].contains(&i) {
                    valid = true;
                }
            } else if num > 0 && valid {
                nums.push(num);
                num = 0;
                valid = false;
            } else {
                num = 0;
                valid = false;
            }
        }
        if num > 0 && valid {
            nums.push(num);
        }
        num = 0;
        valid = false;
    }
    nums
}

#[cfg(test)]
mod tests {
    use super::*;

    const INPUT: &str = "467..114..
...*......
..35..633.
......#...
617*......
.....+.58.
..592.....
......755.
...$.*....
.664.598..";

    #[test]
    fn test_process_part_one() {
        let input_bytes = INPUT.as_bytes();
        assert_eq!(4361, process_part_one(BufReader::new(input_bytes)));
    }

    #[test]
    fn test_process_part_two() {
        let input_bytes = INPUT.as_bytes();
        assert_eq!(467835, process_part_two(BufReader::new(input_bytes)));
    }
}

Python

Questions and comments welcome!

import collections
import re

from .solver import Solver

class Day03(Solver):
  def __init__(self):
    super().__init__(3)
    self.lines = []

  def presolve(self, input: str):
    self.lines = input.rstrip().split('\n')

  def solve_first_star(self):
    adjacent_to_symbols = set()
    for i, line in enumerate(self.lines):
      for j, sym in enumerate(line):
        if sym in ('0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '.'):
          continue
        for di in (-1, 0, 1):
          for dj in (-1, 0, 1):
            adjacent_to_symbols.add((i + di, j + dj))
    numbers = []
    for i, line in enumerate(self. lines):
      for number_match in re.finditer(r'\d+', line):
        is_adjacent_to_symbol = False
        for j in range(number_match.start(), number_match.end()):
          if (i, j) in adjacent_to_symbols:
            is_adjacent_to_symbol = True
        if is_adjacent_to_symbol:
          numbers.append(int(number_match.group()))
    return sum(numbers)

  def solve_second_star(self):
    gear_numbers = collections.defaultdict(list)
    adjacent_to_gears = {}
    for i, line in enumerate(self.lines):
      for j, sym in enumerate(line):
        if sym == '*':
          for di in (-1, 0, 1):
            for dj in (-1, 0, 1):
              adjacent_to_gears[(i + di, j + dj)] = (i, j)
    for i, line in enumerate(self. lines):
      for number_match in re.finditer(r'\d+', line):
        adjacent_to_gear = None
        for j in range(number_match.start(), number_match.end()):
          if (i, j) in adjacent_to_gears:
            adjacent_to_gear = adjacent_to_gears[(i, j)]
        if adjacent_to_gear:
          gear_numbers[adjacent_to_gear].append(int(number_match.group()))
    ratios = []
    for gear_numbers in gear_numbers.values():
      match gear_numbers:
        case [a, b]:
          ratios.append(a * b)
    return sum(ratios)

Language: C#

I aimed at keeping it as simple and short as reasonably possible this time, no overbuilding here!

I even used a goto to let me break out of multiple loops at once 🤮 (I had to look up how they worked!) I would totally fail me in a code review!

internal class Day3 : IRunnable
    {
        public void Run()
        {
            var input = File.ReadAllLines("Days/Three/Day3Input.txt");
            int sum = 0;
            string numStr = "";
            var starMap = new Dictionary<(int,int),List>();
            for (int i = 0; i < input.Length; i++)           
                for (int j = 0; j < input[i].Length; j++)
                {
                    if (char.IsDigit(input[i][j]))                    
                        numStr += input[i][j];                    
                    if (numStr.Length > 0 && (j == input[i].Length - 1 || !char.IsDigit(input[i][j + 1])))
                    {
                        for (int k = Math.Max(0, i - 1); k < Math.Min(i + 2, input.Length); k++)                        
                            for (int l = Math.Max(0, j - numStr.Length); l < Math.Min(j + 2, input[i].Length); l++)                            
                                if (!char.IsDigit(input[k][l]) && input[k][l] != '.')
                                {
                                    sum += int.Parse(numStr);
                                    if (input[k][l] == '*')
                                    {
                                        if (starMap.ContainsKey((k, l)))                                        
                                            starMap[(k, l)].Add(int.Parse(numStr));                                        
                                        else
                                            starMap.Add((k,l),new List { int.Parse(numStr) });
                                    }
                                    goto endSymbSearch;
                                }                           
                    endSymbSearch:
                        numStr = "";
                    }
                }            
            Console.WriteLine("Result1:"+sum.ToString());
            Console.WriteLine("Result2:" + starMap.Where(sm => sm.Value.Count == 2).Sum(sm => sm.Value[0] * sm.Value[1]));
        }
    }

Python solution

just more parsing problems

Python, used a number map to search positions near symbols.

https://github.com/massahud/advent-of-code-2023/blob/main/day03/day03.ipynb

[Rust] Harder one today, for part 1 I ended up getting stuck for a bit since I wasnt taking numbers at the end of lines into account and in part 2 I defined my gears vector in the wrong spot and spent a bit debugging that

use std::fs;

fn part1(input: String) -> u32 {
    let lines = input.lines().collect::>();
    let mut sum = 0;

    for i in 0..lines.len() {
        let mut num = 0;
        let mut valid = false;
        let chars = lines[i].chars().collect::>();

        for j in 0..chars.len() {
            let character = chars[j];
            let parts = ['*', '#', '+', '$', '/', '%', '=', '-', '&', '@'];

            if character.is_digit(10) {
                num = num * 10 + character.to_digit(10).unwrap();

                if i > 0 {
                    if parts.contains(&lines[i - 1].chars().collect::>()[j]) {
                        valid = true;
                    }

                    if j > 0 {
                        if parts.contains(&lines[i - 1].chars().collect::>()[j - 1]) {
                            valid = true;
                        }
                    }

                    if j < chars.len() - 1 {
                        if parts.contains(&lines[i - 1].chars().collect::>()[j + 1]) {
                            valid = true;
                        }
                    }
                }

                if i < lines.len() - 1 {
                    if parts.contains(&lines[i + 1].chars().collect::>()[j]) {
                        valid = true;
                    }

                    if j > 0 {
                        if parts.contains(&lines[i + 1].chars().collect::>()[j - 1]) {
                            valid = true;
                        }
                    }

                    if j < chars.len() - 1 {
                        if parts.contains(&lines[i + 1].chars().collect::>()[j + 1]) {
                            valid = true;
                        }
                    }
                }

                if j > 0 {
                    if parts.contains(&lines[i].chars().collect::>()[j - 1]) {
                        valid = true;
                    }
                }

                if j < chars.len() - 1 {
                    if parts.contains(&lines[i].chars().collect::>()[j + 1]) {
                        valid = true;
                    }
                }
            }
            else {
                if valid == true {
                    sum += num;
                }

                num = 0;
                valid = false;
            }

            if j == chars.len() - 1 {
                if valid == true {
                    sum += num;
                }

                num = 0;
                valid = false;
            }
        }
    }

    return sum;
}

fn part2(input: String) -> u32 {
    let lines = input.lines().collect::>();
    let mut gears: Vec<(usize, usize, u32)> = Vec::new();
    let mut sum = 0;

    for i in 0..lines.len() {
        let mut num = 0;
        let chars = lines[i].chars().collect::>();
        let mut pos: (usize, usize) = (0, 0);
        let mut valid = false;

        for j in 0..chars.len() {
            let character = chars[j];
            let parts = ['*'];

            if character.is_digit(10) {
                num = num * 10 + character.to_digit(10).unwrap();

                if i > 0 {
                    if parts.contains(&lines[i - 1].chars().collect::>()[j]) {
                        valid = true;
                        pos = (i - 1, j);
                    }

                    if j > 0 {
                        if parts.contains(&lines[i - 1].chars().collect::>()[j - 1]) {
                            valid = true;
                            pos = (i - 1, j - 1);
                        }
                    }

                    if j < chars.len() - 1 {
                        if parts.contains(&lines[i - 1].chars().collect::>()[j + 1]) {
                            valid = true;
                            pos = (i - 1, j + 1);
                        }
                    }
                }

                if i < lines.len() - 1 {
                    if parts.contains(&lines[i + 1].chars().collect::>()[j]) {
                        valid = true;
                        pos = (i + 1, j);
                    }

                    if j > 0 {
                        if parts.contains(&lines[i + 1].chars().collect::>()[j - 1]) {
                            valid = true;
                            pos = (i + 1, j - 1);
                        }
                    }

                    if j < chars.len() - 1 {
                        if parts.contains(&lines[i + 1].chars().collect::>()[j + 1]) {
                            valid = true;
                            pos = (i + 1, j + 1);
                        }
                    }
                }

                if j > 0 {
                    if parts.contains(&lines[i].chars().collect::>()[j - 1]) {
                        valid = true;
                        pos = (i, j - 1);
                    }
                }

                if j < chars.len() - 1 {
                    if parts.contains(&lines[i].chars().collect::>()[j + 1]) {
                        valid = true;
                        pos = (i, j + 1);
                    }
                }
            }
            else {
                if valid == true {
                    let mut current_gear = false;
                    
                    for gear in &gears {
                        if gear.0 == pos.0 && gear.1 == pos.1 {
                            sum += num * gear.2;
                            current_gear = true;
                            break;
                        }
                    }
                    
                    if !current_gear {
                        let tuple_to_push = (pos.0.clone(), pos.1.clone(), num.clone());
                        gears.push((pos.0.clone(), pos.1.clone(), num.clone()));
                    }
                }

                num = 0;
                valid = false;
            }

            if j == chars.len() - 1 {
                if valid == true {
                    let mut current_gear = false;
                    
                    for gear in &gears {
                        if gear.0 == pos.0 && gear.1 == pos.1 {
                            sum += num * gear.2;
                            current_gear = true;
                            break;
                        }
                    }
                    
                    if !current_gear {
                        let tuple_to_push = (pos.0.clone(), pos.1.clone(), num.clone());
                        gears.push((pos.0.clone(), pos.1.clone(), num.clone()));
                    }
                }

                num = 0;
                valid = false;
            }
        }
    }

    return sum;
}

fn main() {
    let input = fs::read_to_string("data/input.txt").unwrap();

    println!("{}", part1(input.clone()));
    println!("{}", part2(input.clone()));
}

Code Link

deleted by creator

F# solution

Had an off-by-one error that took me a while to find

Ruby

My goodness I struggled today. https://github.com/snowe2010/advent-of-code/blob/master/ruby_aoc/2023/day03/day03.rb

Dart Solution

Holy moley, if this year is intended to be impervious to AI solution, it’s also working pretty well as a filter to this paltry Human Intelligence.

Find interesting symbols, look around for digits, and expand these into numbers. A dirty hacky solution leaning on a re-used Grid class. Not recommended.

late ListGrid grid;

Index look(Index ix, Index dir) {
  var here = ix;
  var next = here + dir;
  while (grid.isInBounds(next) && '1234567890'.contains(grid.at(next))) {
    here = next;
    next = here + dir;
  }
  return here;
}

/// Return start and end indices of a number at a point.
(Index, Index) expandNumber(Index ix) =>
    (look(ix, Grid.dirs['L']!), look(ix, Grid.dirs['R']!));

int parseNumber((Index, Index) e) => int.parse([
      for (var i = e.$1; i != e.$2 + Grid.dirs['R']!; i += Grid.dirs['R']!)
        grid.at(i)
    ].join());

/// Return de-duplicated positions of all numbers near the given symbols.
nearSymbols(Set syms) => [
      for (var ix in grid.indexes.where((i) => syms.contains(grid.at(i))))
        {
          for (var n in grid
              .near8(ix)
              .where((n) => ('1234567890'.contains(grid.at(n)))))
            expandNumber(n)
        }.toList()
    ];

part1(List lines) {
  grid = ListGrid([for (var e in lines) e.split('')]);
  var syms = lines
      .join('')
      .split('')
      .toSet()
      .difference('0123456789.'.split('').toSet());
  // Find distinct number locations near symbols and sum them.
  return {
    for (var ns in nearSymbols(syms))
      for (var n in ns) n
  }.map(parseNumber).sum;
}

part2(List lines) {
  grid = ListGrid([for (var e in lines) e.split('')]);
  // Look for _pairs_ of numbers near '*' and multiply them.
  var products = [
    for (var ns in nearSymbols({'*'}).where((e) => e.length == 2))
      ns.map(parseNumber).reduce((s, t) => s * t)
  ];
  return products.sum;
}

I get the feeling that I should include some default types for handling 2D maps in my boilerplate, it’s a very recurring problem in AoC after all.

My solution is reasonably simplistic - and therefore also a bit slow, but the design meant I could do part 2 with just a few extra lines of code on the already processed data, here’s the functional part of it; (I push the previous days solution as part of my workflow for starting with the current day so the full code won’t be up until tomorrow)

Point = Struct.new('Point', :x, :y)
PartNumber = Struct.new('PartNumber', :number, :adjacent) do
  def adjacent?(to); adjacent.include?(to); end
  def irrelevant?; adjacent.empty?; end
  def to_i; number; end
end

class Implementation
  def initialize
    @map = []; @dim = { width: 0, height: 0 }; @symbols = []; @numbers = []
  end

  def input(line)
    @dim[:width] = line.size; @dim[:height] += 1
    @map += line.chars
  end

  def calc
    for y in (0..@dim[:height]-1) do
      for x in (0..@dim[:width]-1) do
        chr = get(x, y); next if chr =~ /\d/ || chr == '.'
        @symbols << Point.new(x, y)
      end
    end

    for y in (0..@dim[:height]-1) do
      buf = ""; adj = []
      for x in (0..@dim[:width]) do # Going one over, to fake a non-number as an end char on all lines
        chr = get(x, y)
        if chr =~ /\d/
          buf += chr
          (-1..1).each do |adj_x|
            (-1..1).each do |adj_y|
              next if adj_x == 0 && adj_y == 0 ||
                (x + adj_x < 0) || (x + adj_x >= @dim[:width]) ||
                (y + adj_y < 0) || (y + adj_y >= @dim[:height])
              sym = Point.new(x + adj_x, y + adj_y)
              adj << sym if @symbols.any? sym
            end
          end
        elsif !buf.empty?
          @numbers << PartNumber.new(buf.to_i, adj)
          buf = ""; adj = []
        end
      end
    end
  end

  def output
    part1 = @numbers.reject(&:irrelevant?).map(&:to_i).sum
    puts "Part 1:", part1

    gears = @symbols.select do |sym|
      next unless get(sym) == '*'
      next unless @numbers.select { |num| num.adjacent? sym }.size == 2
      true
    end
    part2 = gears.sum { |gear| @numbers.select { |num| num.adjacent? gear }.map(&:to_i).inject(:*) }

    puts "Part 2:", part2
  end

  private

  def get(x, y = -1)
    y = x.y if x.is_a?(Point)
    x = x.x if x.is_a?(Point)
    return unless (0..@dim[:width]-1).include?(x) && (0..@dim[:height]-1).include?(y)

    @map[y * @dim[:width] + x % @dim[:width]]
  end
end