From cf754c5205bfa6cc1c9d13cb7ae596930822b099 Mon Sep 17 00:00:00 2001
From: Lars Martens <lars@martens.red>
Date: Sat, 11 Dec 2021 11:59:12 +0100
Subject: [PATCH] Day 11

---
 input/11-test.txt |  10 ++++
 input/11.txt      |  10 ++++
 src/bin/11.rs     | 113 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 133 insertions(+)
 create mode 100644 input/11-test.txt
 create mode 100644 input/11.txt
 create mode 100644 src/bin/11.rs

diff --git a/input/11-test.txt b/input/11-test.txt
new file mode 100644
index 0000000..03743f6
--- /dev/null
+++ b/input/11-test.txt
@@ -0,0 +1,10 @@
+5483143223
+2745854711
+5264556173
+6141336146
+6357385478
+4167524645
+2176841721
+6882881134
+4846848554
+5283751526
diff --git a/input/11.txt b/input/11.txt
new file mode 100644
index 0000000..abd8e03
--- /dev/null
+++ b/input/11.txt
@@ -0,0 +1,10 @@
+7612648217
+7617237672
+2853871836
+7214367135
+1533365614
+6258172862
+5377675583
+5613268278
+8381134465
+3445428733
diff --git a/src/bin/11.rs b/src/bin/11.rs
new file mode 100644
index 0000000..20f9c35
--- /dev/null
+++ b/src/bin/11.rs
@@ -0,0 +1,113 @@
+fn main() {
+    let (flashes, sync) = solve();
+    println!("First solution: {}", flashes);
+    println!("Second solution: {}", sync);
+}
+
+fn solve() -> (usize, usize) {
+    let mut field = input();
+    let mut flashes = 0;
+    let mut i = 0;
+
+    loop {
+        i += 1;
+
+        // Add one to each octopus
+        for row in 0..field.len() {
+            for col in 0..field[0].len() {
+                field[row][col].energy += 1;
+            }
+        }
+
+        // Do the flashing
+        let mut changed = true;
+        while changed {
+            changed = false;
+
+            for row in 0..field.len() {
+                for col in 0..field[0].len() {
+                    let current = &mut field[row][col];
+                    if current.energy > 9 && !current.did_flash {
+                        current.did_flash = true;
+                        changed = true;
+                        if i <= 100 {
+                            flashes += 1;
+                        }
+                        for (r, c) in neighbors(row, col) {
+                            field[r][c].energy += 1;
+                        }
+                    }
+                }
+            }
+        }
+
+        // Have all octopi flashed?
+        if field.iter().flat_map(|r| r.iter()).all(|o| o.did_flash) {
+            return (flashes, i);
+        }
+
+        // Reset octopi > 9
+        for row in 0..field.len() {
+            for col in 0..field[0].len() {
+                let current = &mut field[row][col];
+                if current.energy > 9 {
+                    current.energy = 0;
+                    current.did_flash = false;
+                }
+            }
+        }
+    }
+}
+
+fn neighbors(row: usize, col: usize) -> Vec<(usize, usize)> {
+    let mut neighbors = Vec::new();
+
+    let mut rs = vec![row];
+    let mut cs = vec![col];
+
+    if row > 0 {
+        rs.push(row - 1);
+    }
+    if row < 9 {
+        rs.push(row + 1);
+    }
+    if col > 0 {
+        cs.push(col - 1);
+    }
+    if col < 9 {
+        cs.push(col + 1);
+    }
+
+    for r in rs {
+        for &c in &cs {
+            if r == row && c == col {
+                continue;
+            }
+            neighbors.push((r, c));
+        }
+    }
+
+    neighbors
+}
+
+type Field = Vec<Vec<Octopus>>;
+
+struct Octopus {
+    energy: u32,
+    did_flash: bool,
+}
+
+fn input() -> Field {
+    include_str!("../../input/11.txt")
+        .lines()
+        .map(|l| {
+            l.chars()
+                .map(|c| c.to_digit(10).unwrap())
+                .map(|n| Octopus {
+                    energy: n,
+                    did_flash: false,
+                })
+                .collect()
+        })
+        .collect()
+}