From 7b58b9d577b3450f473422cbe4973eae6047088a Mon Sep 17 00:00:00 2001
From: Ishan Jain <contact@ishanjain.me>
Date: Sat, 10 Dec 2022 23:15:15 +0530
Subject: [PATCH] optimized day 10 part 2 by eliminating padded noops and
 repeating the noop block once in addx block

---
 src/main.rs | 66 +++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 46 insertions(+), 20 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index af3df17..57d69c6 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -8,7 +8,6 @@ const INPUTS: [&[u8]; 2] = [
 
 #[derive(Debug)]
 enum Ins {
-    Null,
     Noop,
     Addx(i32),
 }
@@ -17,8 +16,8 @@ fn parse(input: &[u8]) -> Vec<Ins> {
     input
         .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'] => [Ins::Noop, Ins::Null],
+        .map(|line| match &line[0..4] {
+            [b'n', b'o', b'o', b'p'] => Ins::Noop,
             [b'a', b'd', b'd', b'x'] => {
                 let is_neg = line[5] == b'-';
                 let b: i32 = line[5..]
@@ -26,7 +25,7 @@ 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);
 
-                [Ins::Noop, Ins::Addx(if is_neg { -b } else { b })]
+                Ins::Addx(if is_neg { -b } else { b })
             }
             _ => unreachable!(),
         })
@@ -51,26 +50,53 @@ fn solution(input: Vec<Ins>) -> String {
 
     let mut i = 0;
     for ip in input.into_iter() {
-        if let Ins::Null = ip {
-            continue;
-        }
+        match ip {
+            Ins::Noop => {
+                if sprite & ((1 << 63) >> i) > 0 {
+                    line |= (1 << 63) >> i;
+                }
 
-        if sprite & ((1 << 63) >> i) > 0 {
-            line |= (1 << 63) >> i;
-        }
+                cycle += 1;
+                i += 1;
 
-        if let Ins::Addx(v) = ip {
-            register += v;
+                if cycle % 40 == 0 {
+                    answer.push(line);
+                    line = 0;
+                    i = 0;
+                }
+            }
+            Ins::Addx(v) => {
+                // Noop
+                if sprite & ((1 << 63) >> i) > 0 {
+                    line |= (1 << 63) >> i;
+                }
 
-            sprite = (0b111 << 61) >> (register - 1);
-        }
-        cycle += 1;
-        i += 1;
+                cycle += 1;
+                i += 1;
 
-        if cycle % 40 == 0 {
-            answer.push(line);
-            line = 0;
-            i = 0;
+                if cycle % 40 == 0 {
+                    answer.push(line);
+                    line = 0;
+                    i = 0;
+                }
+
+                // Add
+                if sprite & ((1 << 63) >> i) > 0 {
+                    line |= (1 << 63) >> i;
+                }
+
+                register += v;
+                sprite = (0b111 << 61) >> (register - 1);
+
+                cycle += 1;
+                i += 1;
+
+                if cycle % 40 == 0 {
+                    answer.push(line);
+                    line = 0;
+                    i = 0;
+                }
+            }
         }
     }