1 files changed, 96 insertions, 0 deletions
diff --git a/day04/src/main.rs b/day04/src/main.rs
new file mode 100644
index 0000000..0205021
--- /dev/null
+++ b/day04/src/main.rs
@@ -0,0 +1,96 @@
+use std::io;
+
+fn valid(map: &[Vec<char>], x: i32, y: i32) -> bool {
+    if x < 0 {
+        return false;
+    }
+    if y < 0 {
+        return false;
+    }
+    let uy: usize = y.try_into().unwrap();
+    if uy >= map.len() {
+        return false;
+    }
+    let ux: usize = x.try_into().unwrap();
+    if ux >= map[uy].len() {
+        return false;
+    }
+    true
+}
+
+fn is_paper(map: &[Vec<char>], x: i32, y: i32) -> bool {
+    if valid(map, x, y) {
+        let uy: usize = y.try_into().unwrap();
+        let ux: usize = x.try_into().unwrap();
+        return map[uy][ux] == '@';
+    }
+    false
+}
+
+fn adjacent(map: &[Vec<char>], x: i32, y: i32) -> usize {
+    let mut count = 0;
+    for dx in -1..=1 {
+        if is_paper(map, x + dx, y - 1) {
+            count += 1;
+        }
+        if is_paper(map, x + dx, y + 1) {
+            count += 1;
+        }
+    }
+    if is_paper(map, x - 1, y) {
+        count += 1;
+    }
+    if is_paper(map, x + 1, y) {
+        count += 1;
+    }
+    count
+}
+
+fn main() {
+    let mut map: Vec<Vec<char>> = Vec::new();
+
+    loop {
+        let mut buffer = String::new();
+        let bytes = io::stdin().read_line(&mut buffer).unwrap();
+        if bytes == 0 {
+            break;
+        }
+        map.push(buffer.trim_end().chars().collect());
+    }
+
+    let mut total = 0;
+    for y in 0..map.len() {
+        for x in 0..map[y].len() {
+            if is_paper(&map, x.try_into().unwrap(), y.try_into().unwrap())
+                && adjacent(&map, x.try_into().unwrap(), y.try_into().unwrap()) < 4
+            {
+                total += 1;
+            }
+        }
+    }
+
+    println!("{}", total);
+
+    let mut total2 = 0;
+    loop {
+        total = 0;
+        let mut next = map.clone();
+        for y in 0..map.len() {
+            for x in 0..map[y].len() {
+                if is_paper(&map, x.try_into().unwrap(), y.try_into().unwrap())
+                    && adjacent(&map, x.try_into().unwrap(), y.try_into().unwrap()) < 4
+                {
+                    total += 1;
+                    next[y][x] = 'x';
+                }
+            }
+        }
+        if total == 0 {
+            break;
+        }
+        map = next;
+        total2 += total;
+    }
+
+    println!("{}", total2);
+}