我已经使用通常的unique_ptr实现了BST:
class BinarySearchTree
{
public:
struct Node {
Node(int k)
{
key = k;
left = nullptr;
right = nullptr;
}
int key;
// This will auto-destroy all child nodes when this Node is destroyed
std::unique_ptr<Node> left;
std::unique_ptr<Node> right;
};
BinarySearchTree():
m_root(nullptr)
, m_depth(0)
{}
void deleteKey(int key)
{
deleteKeyRec(key, m_root);
}
void deleteKeyRec(int key, std::unique_ptr<Node>& node)
{
if (key == node->key) {
// This node needs to be deleted and replaced with one of its children
if (node->left == nullptr && node->right == nullptr) {
// Node to be deleted has no children
node = nullptr;
}
else if (node->left != nullptr && node->right == nullptr) {
// Only left child present
node = std::move(node->left);
}
else if (node->left == nullptr && node->right != nullptr) {
// Only right child present
node = std::move(node->right);
}
else {
// Both children present, find minimum node in left subtree and replace
auto minNode = findMin(node->left);
node->key = minNode->key;
deleteKeyRec(minNode->key, minNode);
}
}
else if (key < node->key) {
deleteKeyRec(key, node->left);
}
else if (key > node->key) {
deleteKeyRec(key, node->right);
}
}
std::unique_ptr<Node> findMin(std::unique_ptr<Node> & node)
{
Node *current = node.get();
while (current->left) {
current = current->left.get();
}
return std::make_unique<Node>(current);
}
private:
std::unique_ptr<Node> m_root; // Clean-up all children when this object is destroyed
int m_depth;
};
我正在尝试迭代实现findMin(),并使其返回unique_ptr&,因此我可以在deleteKeyRec()中使用它来删除最小节点。但是似乎我无法从findMin()返回unique_ptr&。还有另一种方法来迭代实现findMin()吗?
MSVC的特定错误在findMin()的以下行中: 返回std :: make_unique(current);
错误C2664'BinarySearchTree :: Node :: Node(BinarySearchTree :: Node &&)':无法将参数1从'BinarySearchTree :: Node *'转换为'int'
似乎我不应该使用当前的Node *创建新的unique_ptr。但是那我该如何遍历树呢?
修改后的代码,内含最后一个案例的逻辑:
void deleteKeyRec(int key, std::unique_ptr<Node>& node)
{
if (key == node->key) {
// This node needs to be deleted and replaced with one of its children
if (node->left == nullptr && node->right == nullptr) {
// Node to be deleted has no children
node = nullptr;
}
else if (node->left != nullptr && node->right == nullptr) {
// Only left child present
node = std::move(node->left);
}
else if (node->left == nullptr && node->right != nullptr) {
// Only right child present
node = std::move(node->right);
}
else {
// Both children present, find minimum node in right subtree and replace 'node'
Node *owner = nullptr; // stays one step behind current after first iteration
Node *current = node->right.get();
while (current->left.get()) {
owner = current;
current = current->left.get();
}
//auto minNode = findMin(node->left.get());
node->key = current->key; // transfer the key here, we do not free the memory of this node.
if (owner == nullptr) {
// The right node of 'node' is the correct replacement as it has no children
node->right = nullptr; // delete the node from which key was copied
}
else {
// A left node was found when traversing the right subtree of 'node', so that node's owner now will have no left child!
// This left child thats being deleted has already had its key copied to 'node' via 'current'
owner->left = nullptr; // delete the node from which key was copied
}
}
}
else if (key < node->key) {
deleteKeyRec(key, node->left);
}
else if (key > node->key) {
deleteKeyRec(key, node->right);
}
}
答案 0 :(得分:1)
find
函数应将引用/指针/迭代器返回到找到的元素。它根本不应该返回拥有的指针。同样,它不应该将拥有的指针作为参数。它应该将引用/指针/迭代器带到一个节点上。
每个对象/节点必须完全由一个 std::unique_ptr
拥有。因此,如果您不打算从树中删除找到的节点,则不应将其返回为std::unique_ptr
。
例如:
Node& findMin(const Node& node)
{
Node *current = node.get();
while (current->left) {
current = current->left.get();
}
return *current;
}
您对deleteKeyRec
有相同的问题。该参数不应为std::unique_ptr
。