From b0821bc945933e7f12750cf094688a57c081c86f Mon Sep 17 00:00:00 2001
From: Xiretza <xiretza@xiretza.xyz>
Date: Sun, 10 Apr 2022 16:08:48 +0200
Subject: [PATCH] 2021 day13/rust: add solution

---
 2021/day13/day13_rs/Cargo.toml  |  9 ++++
 2021/day13/day13_rs/src/main.rs | 83 +++++++++++++++++++++++++++++++++
 2 files changed, 92 insertions(+)
 create mode 100644 2021/day13/day13_rs/Cargo.toml
 create mode 100644 2021/day13/day13_rs/src/main.rs

diff --git a/2021/day13/day13_rs/Cargo.toml b/2021/day13/day13_rs/Cargo.toml
new file mode 100644
index 0000000..79b502f
--- /dev/null
+++ b/2021/day13/day13_rs/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "day13_rs"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+nom = "7.1.0"
diff --git a/2021/day13/day13_rs/src/main.rs b/2021/day13/day13_rs/src/main.rs
new file mode 100644
index 0000000..cc9e4e8
--- /dev/null
+++ b/2021/day13/day13_rs/src/main.rs
@@ -0,0 +1,83 @@
+#![warn(clippy::pedantic)]
+use std::collections::HashSet;
+use std::io::{stdin, Read};
+
+use nom::bytes::complete::tag;
+use nom::character::complete::{anychar, newline, u32};
+use nom::combinator::{map, map_opt};
+use nom::multi::many1;
+use nom::sequence::{preceded, separated_pair, terminated};
+
+type Input<'a> = &'a str;
+type IResult<'a, T> = nom::IResult<Input<'a>, T>;
+
+type Point = (usize, usize);
+
+fn point(i: Input) -> IResult<Point> {
+    separated_pair(map(u32, |i| i as usize), tag(","), map(u32, |i| i as usize))(i)
+}
+
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+enum Fold {
+    X(usize),
+    Y(usize),
+}
+
+fn fold(i: Input) -> IResult<Fold> {
+    map_opt(
+        preceded(
+            tag("fold along "),
+            separated_pair(anychar, tag("="), map(u32, |i| i as usize)),
+        ),
+        |(dimension, position)| match dimension {
+            'x' => Some(Fold::X(position)),
+            'y' => Some(Fold::Y(position)),
+            _ => None,
+        },
+    )(i)
+}
+
+fn input(i: Input) -> IResult<(Vec<Point>, Vec<Fold>)> {
+    separated_pair(
+        many1(terminated(point, newline)),
+        newline,
+        many1(terminated(fold, newline)),
+    )(i)
+}
+
+fn do_fold(points: impl Iterator<Item = Point>, fold: Fold) -> HashSet<Point> {
+    let transform = |x, n| if x < n { x } else { n - (x - n) };
+    points
+        .map(|(x, y)| match fold {
+            Fold::X(n) => (transform(x, n), y),
+            Fold::Y(n) => (x, transform(y, n)),
+        })
+        .collect()
+}
+
+fn main() {
+    let mut data = String::new();
+    stdin().lock().read_to_string(&mut data).unwrap();
+    let (points, folds) = input(&data).unwrap().1;
+
+    let mut points: HashSet<_> = points.into_iter().collect();
+    let mut folds = folds.into_iter();
+
+    points = do_fold(points.into_iter(), folds.next().unwrap());
+    println!("{}", points.len());
+
+    for fold in folds {
+        points = do_fold(points.into_iter(), fold);
+    }
+
+    for row in 0..=points.iter().map(|&(_, y)| y).max().unwrap() {
+        for col in 0..=points.iter().map(|&(x, _)| x).max().unwrap() {
+            if points.contains(&(col, row)) {
+                print!("#");
+            } else {
+                print!(".");
+            }
+        }
+        println!();
+    }
+}