From f4cb00ba69836fb7dee4205617d1a43ac22e241e Mon Sep 17 00:00:00 2001
From: Bauke <me@bauke.xyz>
Date: Tue, 14 Dec 2021 20:23:48 +0100
Subject: [PATCH] Solve day 13!

---
 source/day_13/canvas.rs | 69 ++++++++++++++++++++++++++++++++
 source/day_13/mod.rs    | 88 +++++++++++++++++++++++++++++++++++++++++
 source/main.rs          |  2 +
 3 files changed, 159 insertions(+)
 create mode 100644 source/day_13/canvas.rs
 create mode 100644 source/day_13/mod.rs

diff --git a/source/day_13/canvas.rs b/source/day_13/canvas.rs
new file mode 100644
index 0000000..831e319
--- /dev/null
+++ b/source/day_13/canvas.rs
@@ -0,0 +1,69 @@
+use std::{collections::HashSet, fmt::Display};
+
+#[derive(Debug, Hash, PartialEq, Eq)]
+pub struct Point(pub isize, pub isize);
+
+#[derive(Debug)]
+pub enum Fold {
+  Horizontal(isize),
+  Vertical(isize),
+}
+
+#[derive(Debug)]
+pub struct Canvas {
+  pub width: isize,
+  pub height: isize,
+  pub points: HashSet<Point>,
+}
+
+impl Canvas {
+  pub fn fold(self, fold: &Fold) -> Self {
+    let (width, height) = match fold {
+      Fold::Horizontal(amount) => (self.width, *amount),
+      Fold::Vertical(amount) => (*amount, self.height),
+    };
+
+    let mut points = HashSet::new();
+    for Point(x, y) in self.points {
+      if y > height {
+        points.insert(Point(x, height - (y - height)));
+        continue;
+      }
+
+      if x > width {
+        points.insert(Point(width - (x - width), y));
+        continue;
+      }
+
+      points.insert(Point(x, y));
+    }
+
+    Self {
+      width,
+      height,
+      points,
+    }
+  }
+}
+
+impl Display for Canvas {
+  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    for y in 0..self.height {
+      for x in 0..self.width {
+        if x % (self.width / 8) == 0 {
+          write!(f, " ")?;
+        }
+
+        if self.points.contains(&Point(x, y)) {
+          write!(f, "█")?;
+        } else {
+          write!(f, " ")?;
+        }
+      }
+
+      writeln!(f)?;
+    }
+
+    Ok(())
+  }
+}
diff --git a/source/day_13/mod.rs b/source/day_13/mod.rs
new file mode 100644
index 0000000..56b92a7
--- /dev/null
+++ b/source/day_13/mod.rs
@@ -0,0 +1,88 @@
+use std::collections::HashSet;
+
+use color_eyre::{eyre::eyre, Result};
+
+mod canvas;
+
+use canvas::{Canvas, Fold, Point};
+use itertools::Itertools;
+
+pub fn solve() -> Result<()> {
+  let input_data = include_str!("../../data/day_13.txt").trim();
+  println!("Day 13 Part 1: {}", part_1(input_data)?);
+  println!("Day 13 Part 2:\n{}", part_2(input_data)?);
+  Ok(())
+}
+
+fn parse(input: &str) -> Result<(Canvas, Vec<Fold>)> {
+  let mut canvas = Canvas {
+    width: 0,
+    height: 0,
+    points: HashSet::new(),
+  };
+
+  let mut in_folds_section = false;
+  let mut folds = vec![];
+
+  for line in input.lines() {
+    if line == "" {
+      in_folds_section = true;
+      continue;
+    }
+
+    if in_folds_section {
+      let mut split = line.split("=");
+      let is_x_axis = split
+        .next()
+        .map(|s| s.ends_with("x"))
+        .ok_or_else(|| eyre!("Invalid line: {}", line))?;
+
+      let amount = split
+        .next()
+        .map(str::parse)
+        .ok_or_else(|| eyre!("Expected number: {}", line))??;
+
+      if is_x_axis {
+        folds.push(Fold::Vertical(amount));
+      } else {
+        folds.push(Fold::Horizontal(amount));
+      }
+    } else {
+      let (x, y) = line
+        .split(",")
+        .tuples()
+        .next()
+        .ok_or_else(|| eyre!("Invalid line: {}", line))?;
+
+      let x = x.parse()?;
+      let y = y.parse()?;
+      if canvas.width < x {
+        canvas.width = x;
+      }
+
+      if canvas.height < y {
+        canvas.height = y;
+      }
+
+      canvas.points.insert(Point(x, y));
+    }
+  }
+
+  Ok((canvas, folds))
+}
+
+fn part_1(input: &str) -> Result<usize> {
+  let (mut canvas, folds) = parse(input)?;
+  canvas = canvas.fold(&folds[0]);
+  Ok(canvas.points.into_iter().count())
+}
+
+fn part_2(input: &str) -> Result<String> {
+  let (mut canvas, folds) = parse(input)?;
+
+  for fold in folds {
+    canvas = canvas.fold(&fold);
+  }
+
+  Ok(format!("{}", canvas))
+}
diff --git a/source/main.rs b/source/main.rs
index 3787895..1860461 100644
--- a/source/main.rs
+++ b/source/main.rs
@@ -12,6 +12,7 @@ mod day_07;
 mod day_08;
 mod day_09;
 mod day_10;
+mod day_13;
 mod day_14;
 
 fn main() -> Result<()> {
@@ -30,6 +31,7 @@ fn main() -> Result<()> {
     day_08::solve,
     day_09::solve,
     day_10::solve,
+    day_13::solve,
     day_14::solve,
   ];