add: d04

2025/04/p1.rs

@@ -0,0 +1,70 @@
+use std::mem;
+
+fn is_paperroll(slice: &[u8], idx: usize) -> bool {
+    slice.get(idx).is_some_and(|&x| x == b'@')
+}
+
+fn count_rolls_at_postns(
+    slice: &[u8],
+    idx: usize,
+    postns: impl IntoIterator<Item = isize>,
+) -> usize {
+    let mut count = 0;
+    for pos in postns.into_iter() {
+        if is_paperroll(slice, idx.wrapping_add_signed(pos)) {
+            count += 1;
+        }
+    }
+
+    count
+}
+
+#[unsafe(no_mangle)]
+fn challenge_usize(buf: &[u8]) -> usize {
+    let mut prev_line = 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;
+                }
+            }
+        }
+
+        if let Some(pln) = prev_line {
+            let sln = surrounded_line.unwrap();
+
+            for (i, _) in sln.iter().enumerate().filter(|(_, b)| **b == b'@') {
+                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]);
+                if adj_count < 4 {
+                    total += 1;
+                }
+            }
+        }
+
+        prev_line = surrounded_line;
+        surrounded_line = Some(ln);
+    }
+
+    let pln = prev_line.unwrap();
+    let lln = surrounded_line.unwrap();
+    for (i, _) in lln.iter().enumerate().filter(|(_, b)| **b == b'@') {
+        let adj_count =
+            count_rolls_at_postns(pln, i, [-1, 0, 1]) + count_rolls_at_postns(lln, i, [-1, 1]);
+        if adj_count < 4 {
+            total += 1;
+        }
+    }
+
+    total
+}

2025/04/p2.rs

@@ -0,0 +1,93 @@
+use std::mem;
+
+fn is_paperroll(slice: &[u8], idx: usize) -> bool {
+    slice.get(idx).is_some_and(|&x| x == b'@')
+}
+
+fn count_rolls_at_postns(
+    slice: &[u8],
+    idx: usize,
+    postns: impl IntoIterator<Item = isize>,
+) -> usize {
+    let mut count = 0;
+    for pos in postns.into_iter() {
+        if is_paperroll(slice, idx.wrapping_add_signed(pos)) {
+            count += 1;
+        }
+    }
+
+    count
+}
+
+#[unsafe(no_mangle)]
+fn challenge_usize(buf: &[u8]) -> usize {
+    let mut prev_line = None;
+    let mut surrounded_line: Option<&[u8]> = None;
+
+    let mut total = 0;
+
+    let mut cleaned_lines = Vec::new();
+
+    for ln in buf[0..(buf.len() - 1)].split(|&b| b == b'\n') {
+        if let Some(fln) = surrounded_line
+            && prev_line.is_none()
+        {
+            let cleaned_start_idx = cleaned_lines.len();
+            cleaned_lines.extend_from_slice(fln);
+            cleaned_lines.push(b'\n');
+
+            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 {
+                    cleaned_lines[cleaned_start_idx + i] = b'x';
+                    total += 1;
+                }
+            }
+        }
+
+        if let Some(pln) = prev_line {
+            let sln = surrounded_line.unwrap();
+
+            let cleaned_start_idx = cleaned_lines.len();
+            cleaned_lines.extend_from_slice(sln);
+            cleaned_lines.push(b'\n');
+
+            for (i, _) in sln.iter().enumerate().filter(|(_, b)| **b == b'@') {
+                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]);
+                if adj_count < 4 {
+                    cleaned_lines[cleaned_start_idx + i] = b'x';
+                    total += 1;
+                }
+            }
+        }
+
+        prev_line = surrounded_line;
+        surrounded_line = Some(ln);
+    }
+
+    let pln = prev_line.unwrap();
+    let lln = surrounded_line.unwrap();
+
+    let cleaned_start_idx = cleaned_lines.len();
+    cleaned_lines.extend_from_slice(lln);
+    cleaned_lines.push(b'\n');
+
+    for (i, _) in lln.iter().enumerate().filter(|(_, b)| **b == b'@') {
+        let adj_count =
+            count_rolls_at_postns(pln, i, [-1, 0, 1]) + count_rolls_at_postns(lln, i, [-1, 1]);
+        if adj_count < 4 {
+            cleaned_lines[cleaned_start_idx + i] = b'x';
+            total += 1;
+        }
+    }
+
+    if total > 0 {
+        // println!("{}", unsafe { str::from_utf8_unchecked(&cleaned_lines) });
+        total += challenge_usize(&cleaned_lines);
+    }
+
+    total
+}