Complete day 6 part 1

day6/src/main.rs

@@ -1,3 +1,37 @@
+fn find_num_chars_before_marker(chars: &Vec<char>) -> usize {
+    let mut iter = chars.iter().enumerate().peekable();
+
+    for (i, _) in &mut iter {
+        let zero = chars.get(i);
+        let one = chars.get(i + 1);
+        let two = chars.get(i + 2);
+        let three = chars.get(i + 3);
+
+        let mut cursor: Vec<char> = vec![*zero.unwrap(), *one.unwrap(), *two.unwrap(), *three.unwrap()];
+        cursor.sort_unstable();
+
+        // If there's a duplicate character, go forward
+        if cursor[0] == cursor[1] || cursor[1] == cursor[2] || cursor[2] == cursor[3] || i < 4 {
+            continue;
+        }
+
+        // Since we are looking 3 characters farther than the current iteration,
+        // we need to add that to the returned index, plus an extra one, because
+        // the array is zero-indexed
+        return i + 4;
+    }
+
+    panic!("Marker not found");
+}
+
 fn main() {
     let file_str = include_str!("input.txt");
+    let chars: Vec<char> = file_str.chars().collect();
+
+    let chars_before_marker = find_num_chars_before_marker(&chars);
+
+    println!(
+        "Part 1: Number of characters before start-of-packet marker: {}",
+        chars_before_marker
+    );
 }