Which XXX would replace the missing statement in the given RBTreeReplaceChild utility function?

RBTreeReplaceChild(parent, currentChild, newChild) {
if (parent⇢left == currentChild)
return RBTreeSetChild(parent, "left", newChild)
XXX
return RBTreeSetChild(parent, "right", newChild)
return false
}

Question

Which XXX would replace the missing statement in the given RBTreeReplaceChild utility function?

RBTreeReplaceChild(parent, currentChild, newChild) {
   if (parent⇢left == currentChild)
      return RBTreeSetChild(parent, "left", newChild)
   XXX
      return RBTreeSetChild(parent, "right", newChild)
   return false
}

BlackTom AI · Accepted Answer

The question asks which XXX should replace the missing statement in the RBTreeReplaceChild utility function. It provides the code path:

RBTreeReplaceChild(parent, currentChild, newChild) {
   if (parent⇢left == currentChild)
      return RBTreeSetChild(parent, "left", newChild)
   XXX
      return RBTreeSetChild(parent, "right", newChild)
   return false
}

First, we observe the intended control flow: if the currentChild is the left child of parent, we update the left link and return. Otherwise, we should check whether the currentChild is the right child of the parent, and if so, update the right link and return. Finally, if neither side matches, the function returns false.

Option evaluation:
- If the missing line were something like 'if (parent⇢right == currentChild)', this would complete the intended two-branch check: first test left, then test right. This mirrors the structure already present for the left branch and follows the same pattern for the right side, ensuring that only the matching side is updated.
- Any alternative (for example, always updating the right child without checking) would be incorrect because it would perform the update even when the currentChild is not the right child, potentially corrupting the tree structure when currentChild resides on the left or is unrelated.
- Another alternative like 'else' without a condition would break the logic because it would perform the right-child update even if currentChild is neither the left nor the right child, causing unintended modifications.

Contextual understanding: RBTreeReplaceChild aims to replace a specific child of a node. The standard pattern is a conditional check on left, followed by a conditional check on right. If neither matches, return false to indicate that the replacement was not possible because currentChild is not a child of the given parent.

Given that the provided answer option is 'else if (parent⇢right == currentChild)', this aligns with the correct two-branch structure (left check, then right check) and preserves the function’s safety by only mutating the right child when appropriate.

In summary, the missing line should perform a right-child equality check identical in form to the left-check, thereby completing the pair of conditions that cover both possible child positions for the parent.

类似问题

How many children can a node have in a binary tree?

A perfect binary tree has leaves at least a half of the total number of nodes.

How many nodes in a perfect binary tree if the tree has 4 levels?

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