Clean up Day 21

src/bin/day21.rs

@@ -106,18 +106,18 @@ fn bfs(plot: &Plot) -> Vec<u64> {
         distance += 1;
     }
 
-    return distances;
+    distances
 }
 
 fn interpolate(x0: usize, mut ys: [i64; 4], x: usize) -> Option<i64> {
     assert!(x >= x0);
     if x <= x0 + 3 {
-        Some(ys[(x - x0) as usize])
+        Some(ys[x - x0])
     } else {
         let mut f = [0; 4];
 
-        for i in 0..4 {
-            f[i] = ys[0];
+        for coef in &mut f {
+            *coef = ys[0];
             for i in 0..ys.len() - 1 {
                 ys[i] = ys[i + 1] - ys[i];
             }
@@ -125,7 +125,7 @@ fn interpolate(x0: usize, mut ys: [i64; 4], x: usize) -> Option<i64> {
 
         let xa = (x - x0) as i64;
         let xb = xa * (x - x0 - 1) as i64;
-        (f[3] == 0).then_some(f[0] + f[1] * xa as i64 + f[2] * xb / 2)
+        (f[3] == 0).then_some(f[0] + f[1] * xa + f[2] * xb / 2)
     }
 }
 
@@ -153,7 +153,7 @@ fn main() -> Result<()> {
     assert!(plot.height == plot.width);
     let side_length = width;
     let required_scale =
-        |step_count| (step_count - plot.start.0 as usize + side_length) / side_length;
+        |step_count| (step_count - plot.start.0 + side_length) / side_length;
 
     let offset = STEPS_P2 % side_length;
     let max_scale = required_scale(STEPS_P2);
@@ -168,8 +168,8 @@ fn main() -> Result<()> {
 
         plot.scale_to(scale0 + 3);
         let distances = bfs(&plot);
-        for i in 0..4 {
-            sequence[i] = positions(&distances, (offset + i * side_length) as u64) as i64;
+        for (i, seq) in sequence.iter_mut().enumerate() {
+            *seq = positions(&distances, (offset + i * side_length) as u64) as i64;
         }
 
         let mut n = 0;