### re: AoC Day 6: Chronal Coordinates VIEW POST

I want to come back to this exercise after Advent is over and refactor, because I think I could make my solution really nice now, but for right now, I'm delirious and need sleep. Here's what I've got. It's not pretty, but it gets stars and that's all that matters.

``````/// Day 6: Chronal Coordinates
///
/// Calculate Manhattan Distances on the X-Y plane

use std::collections::HashMap;
use std::collections::HashSet;

/// A grid of X-Y coordinates and unclaimed points
///
/// coords is a vector of Coordinates.  Their index is their "ID number"
/// points is a vector of unclaimed points.  Their value is the ID of the
///     closest Coordinate
struct Grid {
coords: Vec<Coordinate>,
points: Vec<Option<usize>>,
width: usize,
height: usize,
}

impl Grid {
pub fn new() -> Self {
Self { coords: vec![], points: vec![], width: 0, height: 0 }
}

/// Loads a grid from text, building each coordinate and calculating
/// most of part 1
pub fn from_text(text: &str) -> Self {
let mut grid = Grid::new();
for line in text.lines() {
let mut coord = Coordinate::from_str(line);
coord.id = grid.coords.len();
grid.coords.push(coord);
}
let (height, width) = grid.bounds();
grid.height = height;
grid.width = width;
grid.points.resize(width*height, None);
grid.calculate_closest_coords();
grid
}

/// Calculates the width and height of the grid
fn bounds(&self) -> (usize, usize) {
let max_row = self.coords.iter().map(|coord| coord.y).max().unwrap();
let max_col = self.coords.iter().map(|coord| coord.x).max().unwrap();
(max_row, max_col)
}

/// For each point on the Grid, calculates the closest Coordinate to
/// that point
///
/// Ties count as nothing!
fn calculate_closest_coords(&mut self) {
for y in 0..self.height {
for x in 0..self.width {
let mut min_dist = self.width + self.height;
for coord in self.coords.iter() {
let dist = coord.manhattan_distance_to(x + 1, y + 1);
if dist < min_dist {
min_dist = dist;
self.points[x + y*self.width] = Some(coord.id);
} else if dist == min_dist {
// It's a tie.  No one gets it
self.points[x + y*self.width] = None;
}
}
}
}
}

/// Checks whether or not a coordinate is internal
///
/// Internal coordinates are completely fenced in by other
/// coordinates.  No infinite boundaries (i.e. not touching the edges)
///
/// This could probably be batched in the contructor rather than done in a loop.
fn is_internal(&self, id: usize) -> bool {
let mut external: HashSet<usize> = HashSet::new();
// Left and right side
for y in 0..self.height {
let left = self.points[0 + y*self.width];
let right = self.points[y*self.width + self.width - 1];
if left.is_some() { external.insert(left.unwrap()); }
if right.is_some() { external.insert(right.unwrap()); }
}

// Top and bottom
for x in 0..self.width {
let top = self.points[x];
let bottom = self.points[x + (self.height - 1)*self.width];
if top.is_some() { external.insert(top.unwrap()); }
if bottom.is_some() { external.insert(bottom.unwrap()); }
}

!external.contains(&id)
}

/// Calculates the area of the internal coordinate that claims the most area
pub fn most_claimed_area(&self) -> usize {
let mut counter: HashMap<usize, usize> = HashMap::new();
for point in self.points.iter() {
if point.is_some() {
*counter.entry(point.unwrap()).or_insert(0) += 1;
}
}
*counter.iter()
.filter(|(id, _count)| self.is_internal(**id))
.map(|(_id, count)| count)
.max().unwrap()
}

/// Counts how many points have a total manhattan distance less than
/// a threshold when checked against all Coordinates
pub fn squares_closer_than(&self, dist: usize) -> usize {
let mut distances: Vec<usize> = vec![];
for y in 0..self.height {
for x in 0..self.width {
let total = self.coords.iter()
.fold(0, |acc, coord| acc + coord.manhattan_distance_to(x, y));
if total < dist {
distances.push(total);
}
}
}
distances.iter().count()
}
}

/// An X-Y coordinate on a Grid
struct Coordinate {
id: usize,
x: usize,
y: usize,
}

impl Coordinate {
pub fn new(x: usize, y: usize) -> Self {
Self { id: 0, x, y }
}

/// Loads data from a line of text, essentially a CSV line
pub fn from_str(text: &str) -> Self {
let mut parts = text.split(',');
let x = parts.next().unwrap().trim().parse().unwrap();
let y = parts.next().unwrap().trim().parse().unwrap();
Self { id: 0, x, y }
}

/// Calculate manhattan distance from here to any X-Y pair
pub fn manhattan_distance_to(&self, x: usize, y: usize) -> usize {
let x1 = self.x as i32;
let x2 = x as i32;
let y1 = self.y as i32;
let y2 = y as i32;
((x2 - x1).abs() + (y2 - y1).abs()) as usize
}
}

/// Part 1
pub fn largest_finite_area(text: &str) -> usize {
let grid = Grid::from_text(text);
grid.most_claimed_area()
}

/// Part 2
pub fn squares_closer_than(text: &str, dist: usize) -> usize {
let grid = Grid::from_text(text);
grid.squares_closer_than(dist)
}
``````
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