Question

所以我用C ++实现了一个AVL。当我测试树函数时，当我尝试执行以下操作时，特定测试失败：

将60插入树
将100插入树中 **现在树应该是这样的：
```
  100(root)
60
```
从树中删除60

**我们期望发生的事情：

    60(root)

但相反，我得到一个段错误。此外，当我尝试删除100，一切都很好！这些是被调用的方法：

void AVL<T, Compare>::Delete(const T& key) {
  Node<T>* node = find(key);
  if (!node) {
    return;
  }
  Node<T>* parent = node->getParent();
  if (node->isLeaf() == 1) {
    leafRemove(node);
    fixBalance(parent);
  } else {
    if ((node->getRight()) && (node->getLeft())) {
      oneChildRemove(node);
    } else {
      twoChildrenRemove(node);
    }
  }
}

加：

void AVL<T, Compare>::twoChildrenRemove(Node<T>* node) {
  Node<T>* swapped = getNodeSuccessor(node);
  Node<T>* ancestor = node->getParent();
  swapNodes(node, swapped);
  if (!(swapped->getLeft()) && (!swapped->getRight())) {
    leafRemove(swapped);
  } else {
    oneChildRemove(swapped);
  }
  if (!ancestor) {
    fixBalance(node);
  } else {
    fixBalance(ancestor);
  }
  return;
}

和

template<class T, class Compare>
void AVL<T, Compare>::oneChildRemove(Node<T>* node) {
  Node<T>* ancestor = node->getParent(); //=100
  Node<T>* branch;
  if (node->getLeft()) {
    branch = node->getLeft(); 
  }
  if (node->getRight()) {
    branch = node->getRight();
  }
  swapNodes(node, branch);
  leafRemove(branch);
  if (!ancestor) {
    fixBalance(node);
  } else {
    fixBalance(ancestor);
  }
}

你能发现问题吗？

Answer 1

您对AVL Tree的理解是错误的。

删除节点时，您的算法应满足以下条件，

1) If x has no children, delete x.
2) If x has one child, delete x and link x's parent to x's child
3) If x has two children, 
      -find x's successor z [the leftmost node in the rightsubtree of x]
      -replace x's contents with z's contents, and 
      -delete z.
      (Note: z does not have a left child, but may have a right child)
      [since z has at most one child, so we use case (1) or (2) to delete z]

我会告诉你这个概念，然后你从那里发展。

void AVL<T, Compare>::oneChildRemove(Node<T>* node) {
      Node<T>* swapped= node->getNodeSuccessor(node); //Get the only child
      Node<T>* ancestor = node->getParent();
      swapNodes(ancestor, swapped); //copy child node(swapped) to point to parent(ancestor)
      leafRemove(node);//Delete the node child
}

void AVL<T, Compare>::twoChildrenRemove(Node<T>* node) {
      Node<T>* ancestor = node->getParent();//Get Parent Node of the node to be deleted.
      Node<T>* rightChild = getRightSuccessor(node);//Get Right Child of the node to be deleted
      Node<T>* leftMostRigthChild = GetLeftMostRightChild(rightChild);//Get Left most child of the right child.
      swapNodes(leftMostRigthChild , ancestor);//copy leftmostrightchild to point to parent

      if (!leftMostRigthChild ->getRight()) { //If no right child for the leftMostRigthChild its leaf node.
           leafRemove(leftMostRigthChild); //So delete it.
      } else {
           oneChildRemove(leftMostRigthChild); //Else it is have one right child and hence call oneChildRemove for the leftMostRigthChild.
      }
      return;
 }

AVL Delete方法很奇怪，C ++

1 个答案: