From 5633d377734d307d6ca4c3955d2f5dbc279a2d36 Mon Sep 17 00:00:00 2001
From: Joseph Montanaro <jfmonty2@gmail.com>
Date: Fri, 31 Dec 2021 08:25:28 -0800
Subject: [PATCH] day 15

---
 2021/src/day15.rs | 105 ++++++++++++++++++++++++++++++++++++++++++++++
 2021/src/lib.rs   |  26 +++++++++++-
 2021/src/main.rs  |   6 +--
 3 files changed, 133 insertions(+), 4 deletions(-)
 create mode 100644 2021/src/day15.rs

diff --git a/2021/src/day15.rs b/2021/src/day15.rs
new file mode 100644
index 0000000..751100b
--- /dev/null
+++ b/2021/src/day15.rs
@@ -0,0 +1,105 @@
+use color_eyre::eyre;
+
+use std::collections::{HashMap, BinaryHeap};
+use std::cmp::{Ord, PartialOrd, Ordering};
+
+use crate::lib::Vec2;
+
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
+struct Node {
+    row: usize,
+    col: usize,
+    cost: usize,
+}
+
+impl Ord for Node {
+    fn cmp(&self, other: &Self) -> Ordering {
+        other.cost.cmp(&self.cost)
+            .then_with(|| self.row.cmp(&other.row))
+            .then_with(|| self.col.cmp(&other.col))
+    }
+}
+
+impl PartialOrd for Node {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+
+fn search(graph: &Vec2<usize>) -> usize {
+    // lifted shamelessly from https://doc.rust-lang.org/std/collections/binary_heap/index.html
+    let mut q = BinaryHeap::new();
+    let start = Node {row: 0, col: 0, cost: 0};
+    q.push(start);
+    let mut costs = HashMap::new();
+
+    while let Some(node) = q.pop() {
+        if node.row == graph.row_count() - 1 && node.col == graph.col_count() - 1 {
+            return node.cost;
+        }
+        if &node.cost > costs.get(&(node.row, node.col)).unwrap_or(&usize::MAX) {
+            continue;
+        }
+
+        for (row, col) in graph.rect_neighbors(node.row, node.col) {
+            let hop_cost = graph.get(row, col);
+            let neighbor = Node {row, col, cost: node.cost + hop_cost};
+            if &neighbor.cost < costs.get(&(row, col)).unwrap_or(&usize::MAX) {
+                q.push(neighbor);
+                costs.insert((row, col), neighbor.cost);
+            }
+        }
+    }
+    panic!("Could not find a path");
+}
+
+
+fn load(data: &str) -> eyre::Result<Vec2<usize>> {
+    let width = data.lines().next().unwrap().len();
+    let mut grid = Vec2::new(width);
+    for line in data.lines() {
+        let chars = line.chars().map(|c| c.to_digit(10).unwrap() as usize);
+        grid.push(chars);
+    }
+    Ok(grid)
+}
+
+
+fn tile(grid: &Vec2<usize>) -> Vec2<usize> {
+    let old_cols = grid.col_count();
+    let new_cols = old_cols * 5;
+    let mut result = Vec2::new(new_cols);
+    for row in grid.rows() {
+        let values = (0..new_cols).map(|i| {
+            let v = row[i % old_cols] + i / old_cols;
+            (v - 1) % 9 + 1
+        });
+        result.push(values);
+    }
+
+    let old_rows = grid.row_count();
+    let new_rows = old_rows * 5;
+    for row_n in old_rows..new_rows {
+        let values = (0..new_cols).map(|c| {
+            let r = row_n % old_rows;
+            let v = result.get(r, c) + row_n / old_rows;
+            (v - 1) % 9 + 1
+        })
+        .collect::<Vec<usize>>();
+        result.push(values.into_iter());
+    }
+    result
+}
+
+
+pub fn run(data: &str) -> eyre::Result<(usize, usize)> {
+    let grid = load(data)?;
+    let grid2 = tile(&grid);
+
+    let one = search(&grid);
+    let two = search(&grid2);
+
+    Ok((one, two))
+}
diff --git a/2021/src/lib.rs b/2021/src/lib.rs
index e725aac..77c970d 100644
--- a/2021/src/lib.rs
+++ b/2021/src/lib.rs
@@ -147,6 +147,26 @@ impl Iterator for NeighborCoords {
 }
 
 
+pub struct RectNeighbors {
+    nc: NeighborCoords,
+}
+
+impl Iterator for RectNeighbors {
+    type Item = (usize, usize);
+    fn next(&mut self) -> Option<Self::Item> {
+        if let Some((row, col)) = self.nc.next() {
+            if row == self.nc.start_row || col == self.nc.start_col {
+                return Some((row, col));
+            }
+            else {
+                return self.next();
+            }
+        }
+        return None
+    }
+}
+
+
 #[allow(dead_code)]
 impl<T> Vec2<T> {
     pub fn new(columns: usize) -> Vec2<T> {
@@ -205,6 +225,10 @@ impl<T> Vec2<T> {
         }
     }
 
+    pub fn rect_neighbors(&self, row: usize, col: usize) -> RectNeighbors {
+        RectNeighbors {nc: self.neighbor_coords(row, col)}
+    }
+
     pub fn get(&self, row: usize, col: usize) -> &T {
         &self.data[self.offset(row, col)]
     }
@@ -258,7 +282,7 @@ impl<T: Display> Display for Vec2<T> {
         for row in self.rows() {
             write!(f, "[")?;
             for (i, v) in row.iter().enumerate() {
-                if i > 0 {write!(f, ", ")?;}
+                if i > 0 {write!(f, "")?;}
                 write!(f, "{}", v)?;
             }
             write!(f, "]\n")?;
diff --git a/2021/src/main.rs b/2021/src/main.rs
index 13e99ea..1c18e6b 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 day14;
+mod day15;
 
 
 fn main() -> eyre::Result<()> {
-    let data = load("data/14.txt")?;
+    let data = load("data/15.txt")?;
 
     let start = Instant::now();
-    let (one, two) = day14::run(&data)?;
+    let (one, two) = day15::run(&data)?;
     let (dur, unit) = format_ns(start.elapsed().as_nanos());
 
     let precision = 2.0 - dur.log10().floor();