From 7b04f00291cb2068f306191a6ad66c777696825d Mon Sep 17 00:00:00 2001
From: Wesley Moore <wes@wezm.net>
Date: Wed, 12 Dec 2018 21:08:54 +1100
Subject: [PATCH] Add day 6 2018 part 1 solution

---
 2018/Cargo.toml      |   1 +
 2018/src/bin/day6.rs | 135 +++++++++++++++++++++++++++++++++++++++----
 2 files changed, 126 insertions(+), 10 deletions(-)

diff --git a/2018/Cargo.toml b/2018/Cargo.toml
index ba10ce8..98138c0 100644
--- a/2018/Cargo.toml
+++ b/2018/Cargo.toml
@@ -2,6 +2,7 @@
 name = "advent-of-code"
 version = "0.1.0"
 authors = ["Wesley Moore <wes@wezm.net>"]
+edition = "2018"
 
 [dependencies]
 chrono = "0.4.6"
diff --git a/2018/src/bin/day6.rs b/2018/src/bin/day6.rs
index 4ba37b2..1cb4232 100644
--- a/2018/src/bin/day6.rs
+++ b/2018/src/bin/day6.rs
@@ -2,12 +2,112 @@
 extern crate lazy_static;
 extern crate regex;
 
+use std::collections::{HashMap, HashSet};
 use std::fs;
 
 use regex::Regex;
 
 #[derive(Debug)]
-struct Coordinate(i32, i32);
+struct Coordinate {
+    x: u32,
+    y: u32,
+}
+
+impl Coordinate {
+    fn distance_to(&self, other: &Coordinate) -> u32 {
+        ((other.x as i32 - self.x as i32).abs() + (other.y as i32 - self.y as i32).abs()) as u32
+    }
+}
+
+#[derive(Debug, Clone)]
+enum Claim {
+    Unclaimed,
+    Claimed { index: usize, distance: u32 },
+    Tied { distance: u32 },
+}
+
+struct Grid {
+    grid: Vec<Claim>,
+    width: usize,
+    height: usize,
+}
+
+impl Grid {
+    fn new(width: usize, height: usize) -> Self {
+        Self {
+            grid: vec![Claim::Unclaimed; width * height],
+            width,
+            height,
+        }
+    }
+
+    fn claim(&mut self, index: usize, coord: &Coordinate) {
+        // loop through the grid, calculate the distance to each point, if it's unclaimed or the
+        // distance is shorter then claim it.
+        for (current_index, claim) in self.grid.iter_mut().enumerate() {
+            let current_coord = index_to_coord(current_index, self.width);
+            let distance = coord.distance_to(&current_coord);
+
+            match claim {
+                Claim::Unclaimed => *claim = Claim::Claimed { index, distance },
+                Claim::Claimed {
+                    distance: claimed_distance,
+                    ..
+                } if *claimed_distance > distance => *claim = Claim::Claimed { index, distance },
+                Claim::Claimed {
+                    distance: claimed_distance,
+                    ..
+                } if *claimed_distance == distance => *claim = Claim::Tied { distance },
+                Claim::Tied {
+                    distance: tied_distance,
+                } if distance < *tied_distance => *claim = Claim::Claimed { index, distance },
+                _ => {}
+            }
+        }
+    }
+
+    fn largest_claimed_area(&self) -> u32 {
+        let areas = self.grid.iter().fold(HashMap::new(), |mut areas, claim| {
+            if let Claim::Claimed { index, .. } = claim {
+                let area = areas.entry(index).or_insert(0u32);
+                *area += 1
+            }
+
+            areas
+        });
+
+        // Exclude indexes that touch the edges as they will be infinite
+        let mut exclude = HashSet::new();
+        for x in 0..self.width {
+            if let Claim::Claimed { index, .. } = self.grid[x] {
+                exclude.insert(index);
+            }
+            if let Claim::Claimed { index, .. } = self.grid[self.width * (self.height - 1) + x] {
+                exclude.insert(index);
+            }
+        }
+        for y in 1..self.height - 1 {
+            if let Claim::Claimed { index, .. } = self.grid[y * self.width] {
+                exclude.insert(index);
+            }
+            if let Claim::Claimed { index, .. } = self.grid[y * self.width + self.width - 1] {
+                exclude.insert(index);
+            }
+        }
+
+        *areas
+            .iter()
+            .filter_map(|(index, area)| {
+                if exclude.contains(index) {
+                    None
+                } else {
+                    Some(area)
+                }
+            })
+            .max()
+            .unwrap()
+    }
+}
 
 fn main() {
     let input = fs::read_to_string("input/day6.txt").expect("input");
@@ -23,22 +123,28 @@ fn main() {
 
 fn part1(coordinates: &[Coordinate]) {
     let max = furthest_coord(coordinates);
-    let grid = vec![None, max.0 * max.1];
+    let mut grid = Grid::new(max.x as usize, max.y as usize);
 
-    // Now fill the grid with the coords...
+    // Claim closest locations for each coord
+    for (index, coord) in coordinates.iter().enumerate() {
+        grid.claim(index, &coord);
+    }
 
+    // Find the one with the most claimed area
+    let area = grid.largest_claimed_area();
+    println!("Part 1 = {}", area);
 }
 
 fn furthest_coord(coordinates: &[Coordinate]) -> Coordinate {
     // There are no negative coords, so assume origin at 0,0
-    let mut max = Coordinate(0, 0);
-    for Coordinate(x, y) in coordinates {
-        if *x > max.0 {
-            max.0= *x;
+    let mut max = Coordinate { x: 0, y: 0 };
+    for Coordinate { x, y } in coordinates {
+        if *x > max.x {
+            max.x = *x;
         }
 
-        if *y > max.1 {
-            max.1 = *y;
+        if *y > max.y {
+            max.y = *y;
         }
     }
 
@@ -51,5 +157,14 @@ fn parse_coord(line: &str) -> Option<Coordinate> {
     }
     let captures = RE.captures(line)?;
 
-    Some(Coordinate(captures[1].parse().ok()?, captures[2].parse().ok()?))
+    Some(Coordinate {
+        x: captures[1].parse().ok()?,
+        y: captures[2].parse().ok()?,
+    })
+}
+
+fn index_to_coord(index: usize, width: usize) -> Coordinate {
+    let x = (index % width) as u32;
+    let y = (index / width) as u32;
+    Coordinate { x, y }
 }