Fix binarySearchTreeNode removing

src/data-structures/tree/binary-search-tree/BinarySearchTreeNode.js

@@ -101,9 +101,10 @@ export default class BinarySearchTreeNode extends BinaryTreeNode {
       if (parent) {
         // Node has a parent. Just remove the pointer to this node from the parent.
         parent.removeChild(nodeToRemove);
+        nodeToRemove.parent = null;
       } else {
         // Node has no parent. Just erase current node value.
-        nodeToRemove.setValue(undefined);
+        nodeToRemove.setValue(null);
       }
     } else if (nodeToRemove.left && nodeToRemove.right) {
       // Node has two children.
@@ -127,14 +128,13 @@ export default class BinarySearchTreeNode extends BinaryTreeNode {
 
       if (parent) {
         parent.replaceChild(nodeToRemove, childNode);
+        childNode.parent = parent;
+        nodeToRemove.parent = null;
       } else {
         BinaryTreeNode.copyNode(childNode, nodeToRemove);
       }
     }
 
-    // Clear the parent of removed node.
-    nodeToRemove.parent = null;
-
     return true;
   }
 

src/data-structures/tree/binary-search-tree/__test__/BinarySearchTreeNode.test.js

@@ -252,4 +252,30 @@ describe('BinarySearchTreeNode', () => {
 
     expect(childNode.parent).toBeNull();
   });
+
+  it('should remove nodes 3,6 in tree 3,6,8', () => {
+    const root = new BinarySearchTreeNode(8);
+
+    root.insert(3);
+    root.insert(6);
+
+    root.remove(3);
+    root.remove(6);
+
+    expect(root.right).toBeNull();
+    expect(root.left).toBeNull();
+  });
+
+  it('should remove nodes 8 in tree 6,8', () => {
+    const root = new BinarySearchTreeNode(8);
+
+    root.insert(6);
+
+    root.remove(8);
+
+    expect(root.right).toBeNull();
+    expect(root.left).toBeNull();
+    expect(root.parent).toBeNull();
+    expect(root.value).toBe(6);
+  });
 });