From 50db6dafd060762b0fe31975da4189675ffae7d9 Mon Sep 17 00:00:00 2001
From: Joseph Montanaro <jfmonty2@gmail.com>
Date: Wed, 29 Dec 2021 07:05:02 -0800
Subject: [PATCH] day 13

---
 2021/src/day13.rs | 131 ++++++++++++++++++++++++++++++++++++++++++++++
 2021/src/lib.rs   |  20 +++++++
 2021/src/main.rs  |   6 +--
 3 files changed, 154 insertions(+), 3 deletions(-)
 create mode 100644 2021/src/day13.rs

diff --git a/2021/src/day13.rs b/2021/src/day13.rs
new file mode 100644
index 0000000..f2a44b7
--- /dev/null
+++ b/2021/src/day13.rs
@@ -0,0 +1,131 @@
+use color_eyre::eyre;
+use eyre::eyre;
+
+use crate::lib::{Vec2, IterExt};
+
+
+enum Direction {
+    Horizontal,
+    Vertical,
+}
+
+struct Line {
+    value: usize,
+    direction: Direction,
+}
+
+
+fn load(data: &str) -> eyre::Result<(Vec2<bool>, Vec<Line>)> {
+    // populate a 1500x1500 grid
+    let mut grid: Vec2<bool> = Vec2::with_capacity(1500, 1500);
+    grid.fill_to_cap(false);
+
+    let mut lines = data.lines();
+    for line in &mut lines {
+        if line == "" {break}
+
+        let (col, row) = line.split(',').map(|s| s.parse::<usize>()).take_pair()?;
+        grid.set(row?, col?, true);
+    }
+
+    // having consumed the coordinates, we can move on to the fold lines
+    let mut folds = Vec::new();
+    for line in lines {
+        let (axis, intercept) = line
+            .split(' ')
+            .nth(2)
+            .ok_or_else(|| eyre!("Invalid fold line statement: {}", line))?
+            .split('=')
+            .take_pair()?;
+
+        let direction = match axis {
+            "x" => Direction::Vertical,
+            "y" => Direction::Horizontal,
+            _ => return Err(eyre!("Invalid axis: {}", axis)),
+        };
+        let value = intercept.parse::<usize>()?;
+
+        folds.push(Line {value, direction});
+    }
+    Ok((grid, folds))
+}
+
+
+fn fold(grid: &Vec2<bool>, line: &Line) -> Vec2<bool> {
+    let mut new_rows = grid.row_count();
+    let mut new_cols = grid.col_count();
+    match line.direction {
+        Direction::Horizontal => new_rows = line.value,
+        Direction::Vertical => new_cols = line.value,
+    }
+
+    let mut new_grid = Vec2::with_capacity(new_rows, new_cols);
+    new_grid.fill_to_cap(false);
+    for row in 0..new_rows {
+        for col in 0..new_cols {
+            if *grid.get(row, col) {
+                new_grid.set(row, col, true);
+            }
+
+            let mut mirror_row = row;
+            let mut mirror_col = col;
+            match line.direction {
+                Direction::Horizontal => mirror_row = 2 * new_rows - row,
+                Direction::Vertical => mirror_col = 2 * new_cols - col,
+            }
+            if mirror_row < grid.row_count() && mirror_col < grid.col_count()
+               && *grid.get(mirror_row, mirror_col)
+            {
+                new_grid.set(row, col, true);
+            }
+        }
+    }
+    new_grid
+}
+
+
+fn show(grid: &Vec2<bool>) {
+    for row in grid.rows() {
+        let line = row.iter().map(|&v| if v {'#'} else {' '}).collect::<String>();
+        println!("[{}]", line);
+    }
+}
+
+
+const SAMPLE: &str = "6,10
+0,14
+9,10
+0,3
+10,4
+4,11
+6,0
+6,12
+4,1
+0,13
+10,12
+3,4
+3,0
+8,4
+1,10
+2,14
+8,10
+9,0
+
+fold along y=7
+fold along x=5";
+
+
+pub fn run(data: &str) -> eyre::Result<(usize, usize)> {
+    let (grid, folds) = load(data)?;
+
+    let mut folded = fold(&grid, &folds[0]);
+    let one = folded.values().filter(|v| **v).count();
+
+    for line in &folds[1..] {
+        folded = fold(&folded, line);
+    }
+
+    show(&folded);
+
+    Ok((one, 0))
+}
\ No newline at end of file
diff --git a/2021/src/lib.rs b/2021/src/lib.rs
index 6787be7..eadc466 100644
--- a/2021/src/lib.rs
+++ b/2021/src/lib.rs
@@ -151,6 +151,10 @@ impl<T> Vec2<T> {
         Vec2 {data: Vec::<T>::new(), columns}
     }
 
+    pub fn with_capacity(rows: usize, columns: usize) -> Vec2<T> {
+        Vec2 {data: Vec::<T>::with_capacity(rows * columns), columns}
+    }
+
     pub fn push<S: IntoIterator<Item=T>>(&mut self, row: S) {
         self.data.extend(row.into_iter());
     }
@@ -213,6 +217,22 @@ impl<T> Vec2<T> {
     }
 }
 
+#[allow(dead_code)]
+impl<T: Copy> Vec2<T> {
+    pub fn fill(&mut self, value: T) {
+        for i in 0..self.data.len() {
+            self.data[i] = value;
+        }
+    }
+    
+    pub fn fill_to_cap(&mut self, value: T) {
+        self.fill(value);
+        for _i in self.data.len()..self.data.capacity() {
+            self.data.push(value);
+        }
+    }
+}
+
 
 impl<T> Index<usize> for Vec2<T> {
     type Output = [T];
diff --git a/2021/src/main.rs b/2021/src/main.rs
index 1696cad..3100cb2 100644
--- a/2021/src/main.rs
+++ b/2021/src/main.rs
@@ -4,14 +4,14 @@ use color_eyre::eyre;
 
 mod lib;
 use lib::load;
-mod day12;
+mod day13;
 
 
 fn main() -> eyre::Result<()> {
-    let data = load("data/12.txt")?;
+    let data = load("data/13.txt")?;
 
     let start = Instant::now();
-    let (one, two) = day12::run(&data)?;
+    let (one, two) = day13::run(&data)?;
     let (dur, unit) = format_ns(start.elapsed().as_nanos());
 
     let precision = 2.0 - dur.log10().floor();