Use big lut instead of weird shifts

Author: EbbDrop

src/day8.rs

@@ -10,29 +10,55 @@ const SIZE: i32 = 12;
 
 const SIZE1: i32 = SIZE + 1;
 
+/// Has the `SIZE` lsb set
+const FIELD_SIZE: u64 = 2u64.pow(SIZE as u32) - 1;
+
 const FREQ_RANGE: usize = (b'z' - b'0' + 1) as usize;
 
 #[aoc(day8, part1)]
-pub fn part1(s: &str) -> u64 {
+pub fn part1(s: &str) -> u32 {
     unsafe { part1_inner(s) }
 }
 
-unsafe fn part1_inner(s: &str) -> u64 {
+const SHIFT_LUT: [u64; (SIZE * SIZE * 2) as usize] = {
+    let mut lut = [0; (SIZE * SIZE * 2) as usize];
+
+    let mut x = 0;
+    while x < SIZE {
+        let mut diff_x = -SIZE + 1;
+
+        let field = 1 << x;
+
+        while diff_x < SIZE {
+            lut[(x * SIZE * 2 + diff_x + SIZE - 1) as usize] = if diff_x.is_positive() {
+                field << diff_x
+            } else {
+                field >> -diff_x
+            };
+
+            diff_x += 1;
+        }
+
+        x += 1;
+    }
+
+    lut
+};
+
+unsafe fn part1_inner(s: &str) -> u32 {
     #[cfg(not(test))]
     const SIZE: i16 = 50;
     #[cfg(test)]
     const SIZE: i16 = 12;
 
     const SIZE1: i16 = SIZE + 1;
+
     let s = s.as_bytes();
 
-    let mut masts: [ArrayVec<[i16; 3]>; FREQ_RANGE] =
-        [ArrayVec::from_array_empty([0; 3]); FREQ_RANGE];
+    let mut masts: [ArrayVec<[(i16, i16); 3]>; FREQ_RANGE] =
+        [ArrayVec::from_array_empty([(0, 0); 3]); FREQ_RANGE];
 
-    let mut antinodes = [false; (SIZE * SIZE) as usize];
-    let mut total_antinotedes = 0;
-
-    // let mut numbers = [0; 5];
+    let mut antinodes = [0u64; SIZE as usize];
 
     for i in unsafe { OneInv::new_unchecked(b'.').iter(s) } {
         if s[i] == b'\n' {
@@ -46,40 +72,45 @@ unsafe fn part1_inner(s: &str) -> u64 {
 
         // numbers[masts[f as usize].len()] += 1;
 
-        for mast_i in &masts[f as usize] {
-            let mast_x = mast_i % SIZE1;
-            let mast_y = mast_i / SIZE1;
-
+        for (mast_y, mast_x) in masts.get_unchecked(f as usize) {
             let diff_x = mast_x - new_x;
             let diff_y = new_y - mast_y;
 
-            let node_x = mast_x + diff_x;
-            if node_x >= 0 && node_x < SIZE && mast_y >= diff_y {
+            if *mast_y >= diff_y {
                 let node_y = mast_y - diff_y;
 
-                total_antinotedes +=
-                    !antinodes.get_unchecked((node_y * SIZE + node_x) as usize) as u64;
-                *antinodes.get_unchecked_mut((node_y * SIZE + node_x) as usize) = true;
+                *antinodes.get_unchecked_mut(node_y as usize) |=
+                    SHIFT_LUT[(mast_x * SIZE * 2 + diff_x + SIZE - 1) as usize];
             }
 
-            let node_x = new_x - diff_x;
-            if node_x >= 0 && node_x < SIZE && new_y + diff_y < SIZE {
+            if new_y + diff_y < SIZE {
                 let node_y = new_y + diff_y;
 
-                total_antinotedes +=
-                    !antinodes.get_unchecked((node_y * SIZE + node_x) as usize) as u64;
-                *antinodes.get_unchecked_mut((node_y * SIZE + node_x) as usize) = true;
+                *antinodes.get_unchecked_mut(node_y as usize) |=
+                    SHIFT_LUT[(new_x * SIZE * 2 - diff_x + SIZE - 1) as usize];
             }
         }
 
-        masts[f as usize].try_push(i);
+        masts[f as usize].try_push((new_y, new_x));
     }
-
-    // for i in 0..5 {
-    //     println!("{i}: {}", numbers[i]);
+    // for y in 0..SIZE {
+    //     for x in 0..SIZE {
+    //         print!(
+    //             "{}",
+    //             if antinodes[y as usize] & 1 << x != 0 {
+    //                 '#'
+    //             } else {
+    //                 s[(y * SIZE1 + x) as usize] as char
+    //             }
+    //         )
+    //     }
+    //     println!("");
     // }
 
-    total_antinotedes
+    antinodes
+        .iter()
+        .map(|field| (field & FIELD_SIZE).count_ones())
+        .sum()
 }
 
 #[aoc(day8, part2)]