[英]Finding the parent of a node in a Binary tree
I am trying to write a method to find the parent of a given node.我正在尝试编写一种方法来查找给定节点的父节点。 Here's my method.这是我的方法。
I created a BinaryNode
object r which initially refers to root.我创建了一个BinaryNode
对象 r,它最初是指根。
public BinaryNode r=root;
public BinaryNode parent(BinaryNode p){
BinaryNode findParent=p;
if (isRoot(findParent) || r==null){
return null;
}
else{
if(r.left==findParent || r.right==findParent)
return r;
else{
if (r.element<findParent.element)
return parent(r.right);
else
return parent(r.left);
}
}
}
THis code doesn't work properly .I think that's because r is a null object.Because when I do这段代码不能正常工作。我认为那是因为 r 是一个空对象。因为当我这样做时
if (isRoot(findParent) || r==null){
System.out.println(r==null);
return null;}
r==null
evaluates to true
.How come that happen because I have inserted nodes as r==null
评估为true
为什么会发生这种情况,因为我已将节点插入为
public static void main (String args[]){
BinaryTree t=new BinaryTree();
t.insert(5);
t.insert(t.root,4);
t.insert(t.root,6);
t.insert(t.root,60);
t.insert(t.root,25);
t.insert(t.root,10);
and the root is not null.并且根不为空。
Can some one please point out why that happens and if what I am trying to do in order to find the parent node is logically correct.有人可以指出为什么会发生这种情况,以及我为了找到父节点而尝试做的事情在逻辑上是否正确。
The problem is that you MUST keep track of your current node, while keeping the node who's parent you want to find.问题是您必须跟踪当前节点,同时保留要查找的父节点。 And as far as I understand your code, you keep the variable, but never change it据我了解你的代码,你保留变量,但永远不要改变它
I'd recommend using a helper function.我建议使用辅助函数。 This would look something like that:这看起来像这样:
public BinaryNode parent(BinaryNode p){
parentHelper(root,p)
}
private BinaryNode parentHelper(BinaryNode currentRoot, BinaryNode p) {
if (isRoot(p) || currentRoot==null){
return null;
}
else{
if(currentRoot.left==p || currentRoot.right==p)
return currentRoot;
else {
if (currentRoot.element<p.element) {
return parentHelper(currentRoot.right,p);
}
else {
return parentHelper(currentRoot.left,p);
}
}
}
}
I compared value to value because I didn't define the way to compare the nodes.我将值与值进行了比较,因为我没有定义比较节点的方式。
public static Node FindParent(Node root, Node node)
{
if (root == null || node == null)
{
return null;
}
else if ( (root.Right != null && root.Right.Value == node.Value) || (root.Left != null && root.Left.Value == node.Value))
{
return root;
}
else
{
Node found = FindParent(root.Right, node);
if (found == null)
{
found = FindParent(root.Left, node);
}
return found;
}
}
使用两个参数:一个用于当前节点,一个用于正在搜索的节点。
Here is code to find out parent node using a stack Data Structures.这是使用堆栈数据结构找出父节点的代码。
Stack<TreeNode> parentStack = new Stack<TreeNode>();
public static void inOrderTraversal(TreeNode root){
if(root != null){
if(parentStack.size()==0){
parentStack.push(root);
}
if(root.getLeftChild()!=null){
parentStack.push(root);
inOrderTraversal(root.getLeftChild());
}
parent = parentStack.pop();
System.out.println(root.getNodeValue()+"'s parent is "+parent.getNodeValue());
if(root.getRightChild()!=null){
parentStack.push(root);
inOrderTraversal(root.getRightChild());
}
}
else{
if(root==null){System.err.println("Can't process a empty root tree");}
}
}
I prefer to delegate as much work as I can to lower-level components, in this case the Node class.我更喜欢将尽可能多的工作委托给较低级别的组件,在这种情况下是 Node 类。 Re: finding a node's parent, this is how I do it ...回复:找到一个节点的父节点,这就是我的做法......
template <typename T>
Node<T>* Node<T>::parent (const Node<T>* node)
{
if (node)
{
if (*node < *this)
{
if (left && (*node < *left))
return left->parent (node);
return this;
}
if (*node > *this)
{
if (right && (*right > *node))
return right->parent (node);
return this;
}
}
return nullptr;
}
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