Implement 2025 - Day 7 - Part 2

2025/07.rs

@@ -1,6 +1,14 @@
 ---cargo
+[profile.dev]
+opt-level = 3
+
+[dependencies]
+nalgebra = "0.34"
 ---
 
+use nalgebra::DMatrix;
+use std::collections::HashMap;
+
 static CONTENT: &'static str = include_str!("./inputs/07_1.txt");
 
 #[derive(Debug, PartialEq)]
@@ -21,47 +29,72 @@ fn main() {
         }).collect::<Vec<_>>()
     }).collect();
 
-    println!("Grid: {:?}", grid);
+    let height = grid.len();
+    let width = grid[0].len();
 
-    // (x, y)
-    let source = grid.iter().enumerate().flat_map(|(y, row)| core::iter::repeat(y).zip(row.iter().enumerate()).map(|(y, (x, c))| (y, x, c))).find_map(|(y, x, c)| (c == &Cell::Sourc).then_some((x, y))).unwrap();
-    println!("Source {:?}", source);
+    let nodes: Vec<(usize, usize)> = grid.iter().enumerate().flat_map(|(y, row)| {
+        core::iter::repeat(y).zip(row.iter().enumerate().filter(|(_, c)| c != &&Cell::Empty)).map(|(y, (x, c))| (x, y))
+    }).chain((0..width).zip(core::iter::repeat(height))).collect();
+    println!("Nodes: {:?}", nodes.len());
+    let node_map: HashMap<(usize, usize), usize> = nodes.iter().copied().enumerate().map(|(idx, v)| (v, idx)).collect();
 
-    let mut splits = 0;
 
-    let mut queue: Vec<(usize, usize)> = vec![(source.0, source.1+1)];
-    while let Some((x, mut y)) = queue.pop() {
-        if grid[y][x] != Cell::Empty {
-            continue;
-        }
+    let mut adj_matrix = DMatrix::from_element(nodes.len(), nodes.len(), 0);
 
+    for (sx, sy) in nodes.iter().copied() {
+        match grid.get(sy).map(|r| &r[sx]) {
+            Some(Cell::Empty) | Some(Cell::TBeam) => unreachable!(),
+            Some(Cell::Sourc) => {
+                let x = sx;
+                let mut y = sy+1;
                 while grid.get(y).map(|r| &r[x]) == Some(&Cell::Empty) {
-            // println!("({}, {})", x, y);
-
-            grid[y][x] = Cell::TBeam;
                     y += 1;
                 }
 
-        match grid.get(y).map(|r| &r[x]) {
-            None => {}
-            Some(Cell::Empty) => unreachable!(),
-            Some(Cell::Sourc) => unreachable!(),
-            Some(Cell::Split) => {
-                // println!("Split");
-                splits += 1;
+                let s_idx = node_map.get(&(sx, sy)).unwrap();
+                let t_idx = node_map.get(&(x, y)).unwrap();
 
-                if let Some(nx) = x.checked_sub(1) {
-                    queue.push((nx, y));
+                adj_matrix[(*s_idx, *t_idx)] = 1;
             }
-                if x+1 < grid[y].len() {
-                    queue.push((x+1, y));
+            Some(Cell::Split) => {
+                for x in [sx-1, sx+1] {
+                    let mut y = sy+1;
+                    while grid.get(y).map(|r| &r[x]) == Some(&Cell::Empty) {
+                        y += 1;
+                    }
+
+                    let s_idx = node_map.get(&(sx, sy)).unwrap();
+                    let t_idx = node_map.get(&(x, y)).unwrap();
+
+                    adj_matrix[(*s_idx, *t_idx)] = 1;
                 }
             }
-            Some(Cell::TBeam) => {
-                println!("Beam");
-            }
+            None => {}
         };
     }
 
-    println!("Splits: {:?}", splits);
+    let source = nodes.iter().copied().find(|(x, y)| matches!(grid.get(*y).map(|r| &r[*x]), Some(Cell::Sourc))).unwrap();
+    println!("Source: {:?}", source);
+
+    // println!("{}", adj_matrix);
+
+    let mut routes = 0;
+    let mut result_matrix = DMatrix::identity(nodes.len(), nodes.len());
+    for i in 1..height {
+        result_matrix *= &adj_matrix;
+
+        let versions = (0..width).map(|x| {
+            let s_idx = node_map.get(&source).unwrap();
+            let t_idx = node_map.get(&(x, height)).unwrap();
+
+            let routes = result_matrix[(*s_idx, *t_idx)];
+
+            routes
+        }).sum::<usize>();
+        println!("[{}] Routes {}", i, versions);
+
+        routes += versions;
+    }
+
+    println!("Total Routes: {:?}", routes);
 }