Which XXX completes the C++ AVL tree Node class's SetChild() function?

bool SetChild(Child whichChild, Node* child) {
if (whichChild == LEFTCHILD) {
left = child;
}
else {
right = child;
}
if (child) {
XXX
}
UpdateHeight();
return true;
}

Question

Which XXX completes the C++ AVL tree Node class's SetChild() function?

bool SetChild(Child whichChild, Node* child) {
   if (whichChild == LEFTCHILD) {
      left = child;
   }
   else {
      right = child;
   }
   if (child) {
      XXX
   }
   UpdateHeight();
   return true;
}

BlackTom AI · Accepted Answer

The question asks which snippet should complete the SetChild() function in a C++ AVL tree Node class.
First, observe what the function currently does: it assigns the given child to either the left or right pointer depending on whichChild, and if a non-null child is provided, it should perform an additional setup before updating the node's height and returning.
Since there are no alternative answer options listed in the provided data, we focus on the logical necessity within the code given.
- After setting left = child or right = child, if a non-null child is being attached, it is important to establish the bi-directional relationship by updating the child's parent pointer. Without this, the child node may not be aware of its new parent, which can lead to incorrect tree navigation, miscomputed heights, or broken invariants during rotations.
- The typical line to insert here is: child->parent = this; This creates the parent link from the child back to the node that now owns it, enabling upward traversal and correct maintenance of subtree relationships during operations like rotations or height updates.
- If (child) is true (i.e., a non-null pointer), performing child->parent = this; ensures that any code that relies on child->parent being valid will function correctly. Conversely, if child is null, we should not attempt to dereference it, hence the guard already provided by if (child).
- After this step, the function proceeds to UpdateHeight(); which relies on the correct child pointers and, importantly, correct parent links for any potential recursion or balance checks that involve parent references.

In summary, the intended completion of the XXX is to set the new child’s parent to the current node, ensuring proper ownership and navigation within the AVL tree structure. Specifically:
- Correct: child->parent = this;
- Incorrect use would neglect establishing the family link, leading to potential inconsistencies in tree properties and rotations.
- The guard if (child) prevents dereferencing a null pointer, so the code remains robust when detaching a child.

Which XXX completes the C++ AVL tree Node class's SetChild() function? bool SetChild(Child whichChild, Node* child) { if (whichChild == LEFTCHILD) { left = child; } else { right = child; } if (child) { XXX } UpdateHeight(); return true; }

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