Day 11

Cargo.toml

@@ -42,3 +42,7 @@ path = "src/day9.rs"
 [[bin]]
 name = "day10"
 path = "src/day10.rs"
+
+[[bin]]
+name = "day11"
+path = "src/day11.rs"

inputs/day11.txt

@@ -0,0 +1,10 @@
+5665114554
+4882665427
+6185582113
+7762852744
+7255621841
+8842753123
+8225372176
+7212865827
+7758751157
+1828544563

src/day11.rs

@@ -0,0 +1,114 @@
+use std::collections::HashSet;
+
+fn square(x: usize, y: usize) -> Vec<(usize, usize)> {
+    let mut sq = Vec::new();
+    if y > 0 {
+        if x > 0 {
+            sq.push((x - 1, y - 1))
+        }
+        sq.push((x, y - 1));
+        if x < 9 {
+            sq.push((x + 1, y - 1))
+        }
+    }
+    if x > 0 {
+        sq.push((x - 1, y))
+    }
+    if x < 9 {
+        sq.push((x + 1, y))
+    }
+    if y < 9 {
+        if x > 0 {
+            sq.push((x - 1, y + 1))
+        }
+        sq.push((x, y + 1));
+        if x < 9 {
+            sq.push((x + 1, y + 1))
+        }
+    }
+    sq
+}
+
+fn step(grid: &mut Vec<Vec<u32>>) -> usize {
+    let mut flashed = HashSet::new();
+
+    loop {
+        let mut new_flashes = false;
+        for (y, row) in grid.iter().enumerate() {
+            for (x, octopus) in row.iter().enumerate() {
+                let adjacent = square(x, y)
+                    .iter()
+                    .filter(|(xx, yy)| flashed.contains(&(*xx, *yy)))
+                    .count() as u32;
+                if (octopus + adjacent + 1) >= 10 && !flashed.contains(&(x, y)) {
+                    flashed.insert((x, y));
+                    new_flashes = true;
+                }
+            }
+        }
+        if !new_flashes {
+            break;
+        }
+    }
+
+    for (y, row) in grid.iter_mut().enumerate() {
+        for (x, octopus) in row.iter_mut().enumerate() {
+            *octopus = if flashed.contains(&(x, y)) {
+                0
+            } else {
+                *octopus
+                    + square(x, y)
+                        .iter()
+                        .filter(|(xx, yy)| flashed.contains(&(*xx, *yy)))
+                        .count() as u32
+                    + 1
+            };
+        }
+    }
+
+    flashed.len()
+}
+
+fn total_flashes(input: &str) -> usize {
+    let mut octopuses = input
+        .lines()
+        .map(|line| {
+            line.chars()
+                .map(|c| char::to_digit(c, 10).unwrap())
+                .collect::<Vec<u32>>()
+        })
+        .collect::<Vec<Vec<u32>>>();
+
+    (0..100).fold(0, |acc, _| acc + step(&mut octopuses))
+}
+
+fn first_simultaneous_step(input: &str) -> usize {
+    let mut octopuses = input
+        .lines()
+        .map(|line| {
+            line.chars()
+                .map(|c| char::to_digit(c, 10).unwrap())
+                .collect::<Vec<u32>>()
+        })
+        .collect::<Vec<Vec<u32>>>();
+
+    let mut s = 0;
+    loop {
+        s += 1;
+        if step(&mut octopuses) == 100 {
+            break;
+        }
+    }
+    s
+}
+
+fn main() {
+    const INPUT: &str = include_str!("../inputs/day11.txt");
+    println!("solution {}", total_flashes(INPUT));
+    println!("solution {}", first_simultaneous_step(INPUT));
+}
+
+#[test]
+fn test_square() {
+    assert_eq!(square(0, 0), vec![(1, 0), (0, 1), (1, 1)]);
+}