day06: Make more generic and add part 2 with it

Part 2 is basically the same just with 14 chars instead of 4.

day06/src/main.rs

@@ -3,23 +3,25 @@ use std::error;
 use std::fs::File;
 use std::io::prelude::*;
 
+const N_CHARS: usize = 14;
+
 fn main() -> Result<(), Box<dyn error::Error>> {
 	let mut f = File::open("input.txt")?;
 
 	let mut buf = [0; 32];
 	let mut pos = 0;
 	let mut found = false;
-	let mut n = f.read(&mut buf[3..])?;
+	let mut n = f.read(&mut buf[(N_CHARS - 1)..])?;
 	while n > 0 {
-		for i in 4..(4 + n) {
+		for i in N_CHARS..(N_CHARS + n) {
 			pos += 1;
-			// println!("{}", std::str::from_utf8(&buf[(i - 4)..i]).unwrap());
+			// println!("{}", std::str::from_utf8(&buf[(i - N_CHARS)..i]).unwrap());
 			// skip if we read uninitialized data from first run
-			if buf[i - 4] == 0 {
+			if buf[i - N_CHARS] == 0 {
 				continue;
 			}
-			let set: HashSet<&u8> = HashSet::from_iter(&buf[(i - 4)..i]);
+			let set: HashSet<&u8> = HashSet::from_iter(&buf[(i - N_CHARS)..i]);
-			if set.len() == 4 {
+			if set.len() == N_CHARS {
 				found = true;
 				break;
 			}
@@ -27,10 +29,10 @@ fn main() -> Result<(), Box<dyn error::Error>> {
 		if found {
 			break;
 		}
-		for i in 0..3 {
+		for i in 0..(N_CHARS - 1) {
-			buf[i] = buf[29 + i];
+			buf[i] = buf[(32 - N_CHARS + 1) + i];
 		}
-		n = f.read(&mut buf[3..])?;
+		n = f.read(&mut buf[(N_CHARS - 1)..])?;
 	}
     println!("Found 4 different chars at position {}", pos);
     Ok(())