perf

2025/04/p1.rs

@@ -1,4 +1,4 @@
-use std::mem;
+// The use of these 2 could be optimized but not fatal performance
 
 fn is_paperroll(slice: &[u8], idx: usize) -> bool {
     slice.get(idx).is_some_and(|&x| x == b'@')
@@ -21,28 +21,40 @@ fn count_rolls_at_postns(
 
 #[unsafe(no_mangle)]
 fn challenge_usize(buf: &[u8]) -> usize {
-    let mut prev_line = None;
+    challenge_usize_inplace(&buf[0..buf.len() - 1])
+}
+
+fn challenge_usize_inplace(buf: &[u8]) -> usize {
+    let mut prev_line: Option<&[u8]> = None;
     let mut surrounded_line: Option<&[u8]> = None;
 
     let mut total = 0;
 
-    for ln in buf[0..(buf.len() - 1)].split(|&b| b == b'\n') {
-        if let Some(fln) = surrounded_line
-            && prev_line.is_none()
-        {
-            for (i, _) in fln.iter().enumerate().filter(|(_, b)| **b == b'@') {
-                let adj_count = count_rolls_at_postns(fln, i, [-1, 1])
-                    + count_rolls_at_postns(ln, i, [-1, 0, 1]);
-                if adj_count < 4 {
-                    total += 1;
+    for ln in buf.split(|&b| b == b'\n') {
+        if let Some(fln) = surrounded_line {
+            if prev_line.is_none() {
+                for i in 0..fln.len() {
+                    if fln[i] != b'@' {
+                        continue;
+                    }
+                    let adj_count = count_rolls_at_postns(fln, i, [-1, 1])
+                        + count_rolls_at_postns(ln, i, [-1, 0, 1]);
+                    if adj_count < 4 {
+                        total += 1;
+                    }
                 }
             }
+            surrounded_line = Some(fln);
         }
 
         if let Some(pln) = prev_line {
             let sln = surrounded_line.unwrap();
 
-            for (i, _) in sln.iter().enumerate().filter(|(_, b)| **b == b'@') {
+            for i in 0..sln.len() {
+                if sln[i] != b'@' {
+                    continue;
+                }
+
                 let adj_count = count_rolls_at_postns(pln, i, [-1, 0, 1])
                     + count_rolls_at_postns(sln, i, [-1, 1])
                     + count_rolls_at_postns(ln, i, [-1, 0, 1]);
@@ -50,15 +62,22 @@ fn challenge_usize(buf: &[u8]) -> usize {
                     total += 1;
                 }
             }
+
+            surrounded_line = Some(sln);
         }
 
-        prev_line = surrounded_line;
+        prev_line = surrounded_line.take();
         surrounded_line = Some(ln);
     }
 
     let pln = prev_line.unwrap();
     let lln = surrounded_line.unwrap();
-    for (i, _) in lln.iter().enumerate().filter(|(_, b)| **b == b'@') {
+
+    for i in 0..lln.len() {
+        if lln[i] != b'@' {
+            continue;
+        }
+
         let adj_count =
             count_rolls_at_postns(pln, i, [-1, 0, 1]) + count_rolls_at_postns(lln, i, [-1, 1]);
         if adj_count < 4 {