Day 6, puzzle 2

src/bin/d6p1.rs

@@ -0,0 +1,8 @@
+use aoc22::{day6, util};
+
+pub fn main() {
+    let input = util::parse_input();
+    let start = day6::parse_datastream(input.as_str(), 4);
+
+    println!("Packet starts after {} characters", start + 1);
+}

src/bin/d6p2.rs

@@ -0,0 +1,8 @@
+use aoc22::{day6, util};
+
+pub fn main() {
+    let input = util::parse_input();
+    let start = day6::parse_datastream(input.as_str(), 14);
+
+    println!("Message starts after {} characters", start + 1);
+}

src/day6.rs

@@ -0,0 +1,19 @@
+use std::collections::{HashSet, VecDeque};
+
+pub fn parse_datastream(stream: &str, n_distinct: usize) -> usize {
+    let mut chars: VecDeque<char> = VecDeque::new();
+    for (i, char) in stream.chars().enumerate() {
+        if i >= n_distinct {
+            chars.pop_front();
+        }
+        chars.push_back(char);
+        if i >= n_distinct - 1 {
+            let char_set: HashSet<char> = chars.iter().map(char::clone).collect();
+            if char_set.len() == n_distinct {
+                return i;
+            }
+        }
+    }
+
+    panic!("Couldn't find a start marker!")
+}

src/lib.rs

@@ -3,4 +3,5 @@ pub mod day2;
 pub mod day3;
 pub mod day4;
 pub mod day5;
+pub mod day6;
 pub mod util;