improve prop range splitting

src/main.rs

@@ -2,6 +2,7 @@ use repr::{Board, Piece};
 
 mod agent;
 mod game;
+mod misc;
 mod repr;
 
 fn main() {

src/misc.rs

@@ -0,0 +1,24 @@
+pub fn split(min: usize, max: usize, x: usize) -> Vec<Vec<usize>> {
+    if min > x || x > max {
+        return Vec::new();
+    }
+    let index = x - min;
+
+    let collected = (min..=max).collect::<Vec<usize>>();
+    let split = collected.split_at(index);
+    let mut one = split.0.to_vec();
+    one.reverse();
+    let mut two = split.1.to_vec();
+    two.remove(0);
+    vec![one, two]
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn split_test() {
+        assert_eq!(split(0, 6, 2), vec![vec![1, 0], vec![3, 4, 5, 6]]);
+    }
+}

src/repr.rs

@@ -1,5 +1,7 @@
 use std::fmt;
 
+use crate::misc::split;
+
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 pub enum Piece {
     Black,
@@ -76,55 +78,50 @@ impl Board {
             return;
         };
 
-        // both ranges expand __from__ the piece
+        for range in split(0, BOARD_SIZE - 1, i) {
-        let i_ranges: Vec<Vec<usize>> =
-            vec![(0..i).rev().collect(), ((i + 1)..BOARD_SIZE).collect()];
-        let j_ranges: Vec<Vec<usize>> =
-            vec![(0..j).rev().collect(), ((j + 1)..BOARD_SIZE).collect()];
-
-        for i_range in i_ranges {
             let mut chain_length: usize = 0;
-            for &new_i in &i_range {
+            for &new_i in &range {
                 let Some(piece) = self.get(new_i, j) else {
                     break;
                 };
                 if piece == &starting_color {
                     if chain_length > 0 {
                         // fill all opposite colors with this color
-                        let Some(i_o_s) = i_range.get(..chain_length) else {
+                        let Some(i_o_s) = range.get(..chain_length) else {
                             break;
                         };
+
+                        // fill all opposite colors with this color
                         for i_o in i_o_s {
                             self.place_and_prop_unchecked(*i_o, j, starting_color);
                         }
                     }
                     break;
-                } else {
-                    chain_length += 1;
                 }
+                chain_length += 1;
             }
         }
 
-        for j_range in j_ranges {
+        for range in split(0, BOARD_SIZE - 1, j) {
             let mut chain_length: usize = 0;
-            for &new_j in &j_range {
+            for &new_j in &range {
                 let Some(piece) = self.get(i, new_j) else {
                     break;
                 };
                 if piece == &starting_color {
                     if chain_length > 0 {
-                        let Some(j_o_s) = j_range.get(..chain_length) else {
+                        let Some(j_o_s) = range.get(..chain_length) else {
                             break;
                         };
+
                         // fill all opposite colors with this color
                         for j_o in j_o_s {
                             self.place_and_prop_unchecked(i, *j_o, starting_color);
                         }
                     }
                     break;
-                } else {
-                    chain_length += 1;
                 }
+                chain_length += 1;
             }
         }
     }