概述:
左耳朵耗子专栏《左耳听风》 用户自发每周完成一个ARTS:
1.Algorithm:每周至少做一个 leetcode 的算法题
2.Review:阅读并点评至少一篇英文技术文章
3.Tip:学习至少一个技术技巧
4.Share:分享一篇有观点和思考的技术文章
这周刷的这道树节点旋转算法题还是有点难度的,关于什么是树节点旋转我结合了下边的这段代码来进行展示:
package 算法部分.综合升级;
import 算法部分.树.BalanceTreeDemo;
/**
* 给定一个单链表,其中的元素按升序排序,请将它转化成平衡二叉搜索树(BST)
*
* @author idea
* @data 2019/9/18
*/
public class ListToTree {
TreeNode root;
class ListNode {
int val;
ListNode next;
ListNode(int x) {
val = x;
next = null;
}
}
class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode(int x) {
val = x;
}
}
public void insert(int val) {
if (this.root == null) {
this.root = new TreeNode(val);
return;
}
TreeNode current = root;
while (true) {
if (val < current.val) {
if (current.left == null) {
current.left = new TreeNode(val);
break;
}
current = current.left;
} else if (val > current.val) {
if (current.right == null) {
current.right = new TreeNode(val);
break;
}
current = current.right;
} else if (current.val == val) {
System.out.println("已经有重复节点了!");
return;
}
}
}
public void readTreeNode(TreeNode treeNode) {
if (treeNode != null) {
System.out.print(treeNode.val + "-->");
} else {
System.out.print("null");
}
}
/**
* 前序遍历 根+左+右
*/
public void preReadNode(TreeNode node) {
if (node == null) {
return;
}
readTreeNode(node);
preReadNode(node.left);
preReadNode(node.right);
}
public TreeNode sortedListToBST(ListNode head) {
return null;
}
/**
* 左左旋
*
* @param root
* @return
*/
private TreeNode leftLeftRoate(TreeNode root) {
if (root == null) {
return null;
}
TreeNode originRoot = root;
TreeNode newRoot = originRoot.left;
TreeNode newLeftChild = newRoot.right;
originRoot.left = newLeftChild;
newRoot.right = originRoot;
return newRoot;
}
/**
* 左右旋
*
* @param root
* @return
*/
private TreeNode rightRightRoate(TreeNode root){
if(root==null){
return null;
}
TreeNode originRoot=root;
TreeNode newRoot=root.left;
TreeNode temp=newRoot.right;
return null;
}
public static void main(String[] args) {
ListToTree listToTree=new ListToTree();
listToTree.insert(8);
listToTree.insert(4);
listToTree.insert(12);
listToTree.insert(2);
listToTree.insert(3);
listToTree.preReadNode(listToTree.root);
TreeNode newNode = listToTree.leftLeftRoate(listToTree.root);
System.out.println();
listToTree.preReadNode(newNode);
}
}