Module advent_of_code_2023::day_3

This is my solution for Advent of Code - Day 3: Gear Ratios

parse_grid turns the plain text 2D grid of characters, in to a list of PartNumbers and a SymbolLookup.

sum_valid_part_numbers solves part one, delegating to has_adjacent_symbol and get_adjacent_points to determine if each number is valid.

sum_gear_ratios solves part two. The key logic is in find_gears which uses

• explode_adjacent_points (which uses get_adjacent_points again) to list all adjacent points
• is_point_a_gear_symbol to filter that list to * symbols that might be gears
• Then turns those that are valid into the expected list of Gears

Structs

• Gear 🔒
  A representation of a gear by the two part numbers that make up its “gear ratio”
• PartNumber 🔒
  Represents a part number as the position of the first digit, and the number it represents

Functions

• explode_adjacent_points 🔒
  Turn a PartNumber into a list of pairs of the (bare number, point) for each point it is adjacent to
• find_gears 🔒
  Return a list of valid gears. A gear is any * symbol with exactly two adjacent PartNumbers.
• get_adjacent_points 🔒
  Return the list of points adjacent to the whole part number that have non-negative co-ordinates
• has_adjacent_symbol 🔒
  Part numbers are valid if adjacent to a symbol
• is_point_a_gear_symbol 🔒
  Returns true if a given 2D co-ordinate maps to a * symbol
• parse_grid 🔒
  Parse a string representing a 2D grid into a list of part numbers and a lookup table of points with character symbols
• run
  The entry point for running the solutions with the ‘real’ puzzle input.
• sum_gear_ratios 🔒
  Solution to part 2 - finds all the valid gears and sums the multiplications of their “gear ratio” numbers.
• sum_valid_part_numbers 🔒
  Solves part 1 - the sum of part numbers next to a symbol

Type Aliases

• Point 🔒
  A point in 2D space
• SymbolLookup 🔒
  A map of 2D points to the part symbol at that point