chore: Move layout-elk to different package

packages/mermaid-layout-elk/src/find-common-ancestor.ts

@@ -0,0 +1,25 @@
+export interface TreeData {
+  parentById: Record<string, string>;
+  childrenById: Record<string, string[]>;
+}
+
+export const findCommonAncestor = (id1: string, id2: string, treeData: TreeData) => {
+  const { parentById } = treeData;
+  const visited = new Set();
+  let currentId = id1;
+  while (currentId) {
+    visited.add(currentId);
+    if (currentId === id2) {
+      return currentId;
+    }
+    currentId = parentById[currentId];
+  }
+  currentId = id2;
+  while (currentId) {
+    if (visited.has(currentId)) {
+      return currentId;
+    }
+    currentId = parentById[currentId];
+  }
+  return 'root';
+};