二叉搜索树我先了解 了解了一天，就是看原理，看网课 ，然后再写的代码，感觉挺难的，但是打完了感觉也不是这么难，就是删除情况有点多，有四种。用JAVA写了一个。
下面的代码只有插入，查找，删除，前序后序中序遍历这几种操作。
package com.company;
public class Main {
public node root;
public node find(int key){ // 查找
if(root == null){
System.out.println("现在的二叉树是一颗空树，找不到任何数据");
return null;
}
node current = root;
while(current.key != key){
if(current.key < key)
current=current.leftchild;
else current = current.rightchild;
if(current == null)
return null;
}
return current;
}
public boolean insert(node data){ //插入节点
if(root == null){
root = data;
return true;
}
if(this.find(data.key) != null){
System.out.println("The number has already exists");
return false;
}
node current = root;
while(current != null){
while(current != null){
if(data.key > current.key){
if(current.rightchild == null){
current.rightchild = data;
return true;
}
current = current.rightchild;
}
else{
if(current.leftchild == null){
current.leftchild = data;
return true;
}
current = current.leftchild;
}
}
}
return false;
}
public void inorder_iterator(node data){ // 中序遍历
if(data.leftchild != null)
this.inorder_iterator(data.leftchild);
System.out.print(data.key+ " ");
if(data.rightchild != null)
this.inorder_iterator(data.rightchild);
}
public void preorder_iterator(node data) { // 前序遍历
System.out.print(data.key + " ");
if (data.leftchild != null)
this.preorder_iterator(data.leftchild);
if (data.rightchild != null)
this.preorder_iterator(data.rightchild);
}
public void postorder_iterator(node data){ // 后序遍历
if(data.leftchild != null)
this.postorder_iterator(data.leftchild);
if(data.rightchild != null)
this.postorder_iterator(data.rightchild);
System.out.print(data.key + " ");
}
public node getMinNode(node data){ //获得最小值
if(data.leftchild == null){
return data;
}
node current = data.leftchild;
while(current.leftchild != null){
current = current.leftchild;
}
return current;
}
public node getMaxNode(node data){ // 获得最大值
if(data.rightchild == null)
return data;
node current = data.rightchild;
while(current.rightchild != null){
current = current.rightchild;
}
return current;
}
public boolean delete(int key){
if(root == null){
System.out.println("这棵树是一颗空树");
return false;
}
node targetParent = root;
node target = root;
boolean isLeftChild = true;
while(target.key != key){
if(key < target.key){
targetParent=target;
target = target.leftchild;
isLeftChild = true;
}
else{
targetParent =target;
target = target.rightchild;
isLeftChild = false;
}
if(target == null)
break;
}
if(target == null){
System.out.println("未发现该值!");
return false;
}
//第一种情况 被删除的节点是叶节点
if(target.leftchild == null && target.rightchild == null){
if(root.key == target.key) {
root = null;
return true;
}
if(isLeftChild)
targetParent.leftchild = null;
else
targetParent.rightchild = null;
}
//第二种情况 被删除的节点只有一个子节点 且这个节点是右节点
else if(target.leftchild == null && target.rightchild != null){
if(target.key == root.key) {
root = root.rightchild;
return false;
}
if(isLeftChild)
targetParent.leftchild = target.rightchild;
else
targetParent.rightchild = target.rightchild;
}
//第三种情况 被删除的节点只有一个子节点 且这个节点是 左节点
else if(target.leftchild != null && target.rightchild == null){
if(target.key == root.key){
root = root.leftchild;
return true;
}
if(isLeftChild)
targetParent.leftchild = target.leftchild;
else
targetParent.rightchild = target.leftchild;
}
//第四种情况 被删除的节点有两个子节点
else {
node nextNode = this.getNextNode(target);
if(target.key == root.key)
root=nextNode;
else if(isLeftChild)
targetParent.leftchild=nextNode;
else
targetParent.rightchild=nextNode;
nextNode.leftchild=target.leftchild;
nextNode.rightchild=target.rightchild;
}
return true;
}
public node getNextNode(node data){ // 找后继节点，即第一个比要删除的节点大的点
node parent = data;
node current = data.rightchild;
while(current.leftchild != null){
parent = current;
current = current.leftchild;
}
if(data.rightchild.key == current.key)
parent.rightchild = current.rightchild;
else
parent.leftchild = current.rightchild;
return current;
}
public static void main(String[] args) {
Main bst = new Main();
node t1 = new node(10);
node t2 = new node(11);
node t3 = new node(8);
node t4 = new node(9);
node t5 = new node(12);
bst.insert(t1);
bst.insert(t2);
bst.insert(t3);
bst.insert(t4);
bst.insert(t5);
bst.inorder_iterator(bst.root);
bst.delete(10);
System.out.println();
bst.inorder_iterator(bst.root);
}
}