Reuse config on last branch

src/segment.rs

@@ -175,22 +175,9 @@ impl Configs {
         reached.len() == self.seg
     }
 
-    fn branch(
-        &mut self,
-        Config { state, tape, .. }: Config,
-        prog: &AnalyzedProg,
-    ) {
-        for &next_state in &prog.diffs[&state] {
-            let Some(init) = self.check_seen(next_state, &tape) else {
-                continue;
-            };
-
-            let next_tape = tape.clone();
-
-            let config = Config::new(next_state, next_tape, init);
-
-            self.add_todo(config);
-        }
+    fn branch(&mut self, mut config: Config, prog: &AnalyzedProg) {
+        let tape = &config.tape;
+        let state = config.state;
 
         let shift = !tape.side();
 
@@ -208,6 +195,33 @@ impl Configs {
 
             self.add_todo(config);
         }
+
+        let Some((last_next, diffs)) = prog.diffs[&state].split_last()
+        else {
+            return;
+        };
+
+        for &next_state in diffs {
+            let Some(init) = self.check_seen(next_state, tape) else {
+                continue;
+            };
+
+            let next_tape = tape.clone();
+
+            let config = Config::new(next_state, next_tape, init);
+
+            self.add_todo(config);
+        }
+
+        if let Some(init) = self.check_seen(*last_next, tape) {
+            config.state = *last_next;
+
+            if init {
+                config.init = init;
+            }
+
+            self.add_todo(config);
+        }
     }
 }
 

src/tree.rs

@@ -556,12 +556,12 @@ fn test_segment() {
     assert_segment_results![
         ((2, 2), 1, (10, 36)),
         //
-        ((3, 2), 1, (1_035, 3_140)),
+        ((3, 2), 1, (1_034, 3_140)),
         //
         ((2, 3), 1, (690, 2_447)),
         //
-        ((4, 2), 1, (145_473, 467_142)),
+        ((4, 2), 1, (145_395, 467_142)),
         //
-        ((2, 4), 1, (119_092, 312_642)),
+        ((2, 4), 1, (119_027, 312_642)),
     ];
 }

test/prog_data.py

@@ -1669,7 +1669,6 @@
     "1RB ...  1LC 1RA  1LA 0LC",
     "1RB 0LB  1LC 1RB  ... 1LA",
     "1RB 0LC  0LC 1RA  ... 1LA",
-    "1RB 0LC  0RC ...  1LC 0RA",
     "1RB 1LC  0LA 0RB  1LA ...",
 
     "1RB 2LA 3RB 0RB  0LB 1LA 2RB ...",