Use mutable reachability rows in isolated SCC probe

crates/oa-core/examples/auto_layout_probe/condensed.rs

@@ -22,14 +22,14 @@ fn charge(work: &mut usize, count: usize) -> Result<(), ModelError> {
 fn components(arcs: &[BTreeSet<usize>], work: &mut usize) -> Result<Vec<Vec<usize>>, ModelError> {
     let n = arcs.len();
     let mut reach = vec![vec![false; n]; n];
-    for start in 0..n {
+    for (start, reachable) in reach.iter_mut().enumerate() {
         let mut todo = vec![start];
-        reach[start][start] = true;
+        reachable[start] = true;
         while let Some(at) = todo.pop() {
             for &next in &arcs[at] {
                 charge(work, 1)?;
-                if !reach[start][next] {
-                    reach[start][next] = true;
+                if !reachable[next] {
+                    reachable[next] = true;
                     todo.push(next);
                 }
             }
@@ -583,6 +583,5 @@ mod tests {
             positions,
             vec![Position { x: 0.0, y: 0.0 }, Position { x: 0.0, y: 216.0 }]
         );
-        assert!(224.0_f32 / 376.0 > 0.5);
     }
 }