day six

06/main.rs

@@ -0,0 +1,85 @@
+#![allow(dead_code)]
+use std::collections::VecDeque;
+use std::fs::File;
+use std::io;
+use std::io::BufRead;
+use std::path::Path;
+use std::time::Instant;
+
+fn main() {
+    let now = Instant::now();
+    part_one();
+    let part_one_duration = now.elapsed();
+    part_two();
+    let part_two_duration = now.elapsed();
+    println!(
+        "p1: {}ms, p2: {}ms",
+        part_one_duration.as_millis(),
+        (part_two_duration - part_one_duration).as_millis()
+    );
+}
+
+fn read_lines<P>(filename: P) -> io::Result<io::Lines<io::BufReader<File>>>
+where
+    P: AsRef<Path>,
+{
+    // note that this discards a final newline
+    let file = File::open(filename)?;
+    Ok(io::BufReader::new(file).lines())
+}
+
+fn part_one() {
+    if let Ok(mut lines) = read_lines("./inputs/input") {
+        if let Some(Ok(signal)) = lines.next() {
+            let mut buf = VecDeque::<char>::new();
+            for (i, c) in signal.chars().enumerate() {
+                if buf.len() < 3 {
+                    // start of stream
+                    buf.push_back(c);
+                    continue;
+                } else if buf.contains(&c)
+                    || buf[0] == buf[1]
+                    || buf[1] == buf[2]
+                    || buf[2] == buf[0]
+                {
+                    // repeated character
+                    buf.pop_front();
+                    buf.push_back(c);
+                } else {
+                    // found it; offset to the next character
+                    println!("{}", i + 1);
+                    return;
+                }
+            }
+        }
+    }
+}
+
+fn part_two() {
+    if let Ok(mut lines) = read_lines("./inputs/input") {
+        if let Some(Ok(signal)) = lines.next() {
+            let mut buf = VecDeque::<char>::new();
+            for (i, c) in signal.chars().enumerate() {
+                if buf.len() < 13 {
+                    // start of stream
+                    buf.push_back(c);
+                    continue;
+                } else if buf.contains(&c)
+                    || (1..buf.len()).any(|i| {
+                        buf.range(i..)
+                            .collect::<VecDeque<&char>>()
+                            .contains(&&buf[i - 1]) // neat trick
+                    })
+                {
+                    // repeated character
+                    buf.pop_front();
+                    buf.push_back(c);
+                } else {
+                    // found it; offset to the next character
+                    println!("{}", i + 1);
+                    return;
+                }
+            }
+        }
+    }
+}