我在二叉搜索树中有以下用于插入和删除的java代码。但这是我第一次使用java,并希望在我可以使用Google概念之前寻求某些方面的帮助。
public class BinarySearchTree {
public static Node root;
public BinarySearchTree(){
this.root = null;
}
public boolean find(int id){
Node current = root;
while(current!=null){
if(current.data==id){
return true;
}else if(current.data>id){
current = current.left;
}else{
current = current.right;
}
}
return false;
}
public boolean delete(int id){
Node parent = root;
Node current = root;
boolean isLeftChild = false;
while(current.data!=id){
parent = current;
if(current.data>id){
isLeftChild = true;
current = current.left;
}else{
isLeftChild = false;
current = current.right;
}
if(current ==null){
return false;
}
}
//if i am here that means we have found the node
//Case 1: if node to be deleted has no children
if(current.left==null && current.right==null){
if(current==root){
root = null;
}
if(isLeftChild ==true){
parent.left = null;
}else{
parent.right = null;
}
}
//Case 2 : if node to be deleted has only one child
else if(current.right==null){
if(current==root){
root = current.left;
}else if(isLeftChild){
parent.left = current.left;
}else{
parent.right = current.left;
}
}
else if(current.left==null){
if(current==root){
root = current.right;
}else if(isLeftChild){
parent.left = current.right;
}else{
parent.right = current.right;
}
}else if(current.left!=null && current.right!=null){
//now we have found the minimum element in the right sub tree
Node successor = getSuccessor(current);
if(current==root){
root = successor;
}else if(isLeftChild){
parent.left = successor;
}else{
parent.right = successor;
}
successor.left = current.left;
}
return true;
}
public Node getSuccessor(Node deleleNode){
Node successsor =null;
Node successsorParent =null;
Node current = deleleNode.right;
while(current!=null){
successsorParent = successsor;
successsor = current;
current = current.left;
}
//check if successor has the right child, it cannot have left child for sure
// if it does have the right child, add it to the left of successorParent.
// successsorParent
if(successsor!=deleleNode.right){
successsorParent.left = successsor.right;
successsor.right = deleleNode.right;
}
return successsor;
}
public void insert(int id){
Node newNode = new Node(id);
if(root==null){
root = newNode;
return;
}
Node current = root;
Node parent = null;
while(true){
parent = current;
if(id<current.data){
current = current.left;
if(current==null){
parent.left = newNode;
return;
}
}else{
current = current.right;
if(current==null){
parent.right = newNode;
return;
}
}
}
}
public void display(Node root){
if(root!=null){
display(root.left);
System.out.print(" " + root.data);
display(root.right);
}
}
public static void main(String arg[]){
BinarySearchTree b = new BinarySearchTree();
b.insert(3);b.insert(8);
b.insert(1);b.insert(4);b.insert(6);b.insert(2);b.insert(10);b.insert(9);
b.insert(20);b.insert(25);b.insert(15);b.insert(16);
System.out.println("Original Tree : ");
b.display(b.root);
System.out.println("");
System.out.println("Check whether Node with value 4 exists : " + b.find(4));
System.out.println("Delete Node with no children (2) : " + b.delete(2));
b.display(root);
System.out.println("\n Delete Node with one child (4) : " + b.delete(4));
b.display(root);
System.out.println("\n Delete Node with Two children (10) : " + b.delete(10));
b.display(root);
}
}
class Node{
int data;
Node left;
Node right;
public Node(int data){
this.data = data;
left = null;
right = null;
}
}
我有两个问题如下
public class BinarySearchTree {
public static Node root = null;
...
}
答案 0 :(得分:9)
拥有static
成员变量意味着它属于类本身,而不是特定成员。换句话说,它在所有实例之间共享。现在我们明白了,很清楚为什么拥有static
根成员是一个有问题的设计 - 它不允许你有两个断开连接的树,因为它们都共享相同的根节点。
如果确实如此,root
肯定应该内联(private static Node root = null;
)而不是构造函数初始化。在构造函数中使用此逻辑意味着每次创建新树 all 时,现有树将失去其根。
答案 1 :(得分:3)
必须仔细考虑使用静态成员,因为正如您所说,BinarySearchTree
创建的所有实例始终存在相同的实例。因此,在您的代码中,root
每次创建新实例时都会重置为null。因此,不要这样做。
您实际上可以像您建议的那样初始化您定义它的root
。
但是,通过删除root
关键字或将树的数据结构与搜索算法分开,使BinarySearchTree
成为static
的成员是更好的做法。然后,您将root
元素作为参数传递给方法。
从数据的角度考虑整个事物 - 您要搜索的树,由它的根节点表示 - 以及对数据进行操作的服务。该服务不应该以紧密的方式与数据绑定:您应该能够使用相同的服务来处理不同的输入数据集。