suspiciously straightforward

2022/Cargo.toml

@@ -27,6 +27,10 @@ path = "src/day4.rs"
 name = "day5"
 path = "src/day5.rs"
 
+[[bin]]
+name = "day6"
+path = "src/day6.rs"
+
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 

2022/src/day6.rs

@@ -0,0 +1,58 @@
+// const DATA: &'static str = "zcfzfwzzqfrljwzlrfnpqdbhtmscgvjw";
+const DATA: &'static str = include_str!("../data/day6.txt");
+
+
+struct CharCounts {
+    chars: [u8; 26],
+}
+
+impl CharCounts {
+    fn new() -> Self {
+        CharCounts { chars: [0; 26]}
+    }
+
+    fn idx(c: u8) -> usize {
+        (c as usize) - (b'a' as usize)
+    }
+
+    fn inc(&mut self, c: u8) {
+        self.chars[Self::idx(c)] += 1;
+    }
+
+    fn dec(&mut self, c: u8) {
+        self.chars[Self::idx(c)] -= 1;
+    }
+
+    fn max(&self) -> u8 {
+        // max only returns None if the iterator is empty
+        *self.chars.iter().max().unwrap()
+    }
+}
+
+
+fn find_marker(data: &[u8], window_size: usize) -> Option<usize> {
+    let mut window = CharCounts::new();
+    for (i, v) in data.iter().enumerate() {
+        window.inc(*v);
+        if i > (window_size - 1) {
+            let dropout = data[i - window_size];
+            window.dec(dropout);
+        }
+
+        if i > (window_size - 1) && window.max() == 1 {
+            return Some(i + 1);
+        }
+    }
+    None
+}
+
+
+fn main() {
+    let bytes = DATA.trim().as_bytes();
+    
+    let m1 = find_marker(&bytes, 4).unwrap();
+    println!("Part 1: {m1}");
+
+    let m2 = find_marker(&bytes, 14).unwrap();
+    println!("Part 2: {m2}");
+}