Add another Null instruction which doesn't do _anything_

This is so we can return an array while parsing rather than a vector
Reduces runtime by 1 microsecond

src/main.rs

@@ -8,6 +8,7 @@ const INPUTS: [&[u8]; 2] = [
 
 #[derive(Debug)]
 enum Ins {
+    Null,
     Noop,
     Addx(i32),
 }
@@ -17,7 +18,7 @@ fn parse(input: &[u8]) -> Vec<Ins> {
         .split(|&c| c == b'\n')
         .filter(|c| !c.is_empty())
         .flat_map(|line| match &line[0..4] {
-            [b'n', b'o', b'o', b'p'] => vec![Ins::Noop],
+            [b'n', b'o', b'o', b'p'] => [Ins::Noop, Ins::Null],
             [b'a', b'd', b'd', b'x'] => {
                 let is_neg = line[5] == b'-';
                 let b: i32 = line[5..]
@@ -25,7 +26,7 @@ fn parse(input: &[u8]) -> Vec<Ins> {
                     .filter(|&&c| (b'0'..=b'9').contains(&c))
                     .fold(0, |a, &x| (a * 10) + (x - b'0') as i32);
 
-                vec![Ins::Noop, Ins::Addx(if is_neg { -b } else { b })]
+                [Ins::Noop, Ins::Addx(if is_neg { -b } else { b })]
             }
             _ => unreachable!(),
         })
@@ -50,17 +51,18 @@ fn solution(input: Vec<Ins>) -> String {
 
     let mut i = 0;
     for ip in input.into_iter() {
+        if let Ins::Null = ip {
+            continue;
+        }
+
         if sprite & ((1 << 63) >> i) > 0 {
             line |= (1 << 63) >> i;
         }
 
-        match ip {
-            Ins::Noop => {}
-            Ins::Addx(v) => {
-                register += v;
+        if let Ins::Addx(v) = ip {
+            register += v;
 
-                sprite = (0b111 << 61) >> (register - 1);
-            }
+            sprite = (0b111 << 61) >> (register - 1);
         }
         cycle += 1;
         i += 1;