24.输入一个二叉搜索树，将该树转换为一个排序的双向链表

package java2019;

import java.util.Stack;

//输入一个二叉搜索树，将该树转换为一个排序的双向链表（不创建新的节点，只能调整树中节点指针的指向）
//核心是中序遍历非递归算法
//修改当前遍历节点与前一遍节点的指针指向
public class Demo24 {
	//中序非递归算法
	public void InorderTravel(TreeNode root){
		Stack<TreeNode> stack = new Stack<TreeNode>();
		TreeNode p = root;
		while(p!=null||!stack.empty()){
			while(p!=null){   //一直向左并将沿途节点压入堆栈
				stack.push(p);
				p=p.left;
			}
			p=stack.pop();
			System.out.println(p.val+" ");
			p=p.right;
		}
	}
	//前序非递归算法
	public void PreorderTravel(TreeNode root){
		Stack<TreeNode> stack = new Stack<TreeNode>();
		TreeNode p = root;
		while(p!=null||!stack.empty()){
			while(p!=null){   //一直向左并将沿途节点压入堆栈
				System.out.println(p.val+" ");
				stack.push(p);
				p=p.left;
			}
			p=stack.pop();
			p=p.right;
		}
		
	}
	//非递归版
	public TreeNode ConvertBSToBiList(TreeNode root){
		if(root==null)
			return null;
		Stack<TreeNode> stack = new Stack<TreeNode>();
		TreeNode p = root;
		TreeNode pre = null; //用于保存中序遍历的上一结点
		boolean isFirst = true;
		while(p!=null || !stack.empty()){
			while(p!=null){
				stack.push(p);
				p=p.left;
			}
			p=stack.pop();
			if(isFirst){
				root=p;//将中序遍历的第一个节点记为root
				pre=root;
				isFirst=false;
			}else{
				pre.right=p;
				p.left=pre;
				pre=p;
			}
			p=p.right;
		}
		return root;
	}
public static void main(String[] args) {
	TreeNode root = new TreeNode(5);
	TreeNode n1 = new TreeNode(3);
	TreeNode n2 = new TreeNode(10);
	TreeNode n3 = new TreeNode(1);
	TreeNode n4 = new TreeNode(4);
	TreeNode n5 = new TreeNode(6);
	TreeNode n6 = new TreeNode(11);
	
	root.left=n1;
	root.right=n2;
	n1.left=n3;
	n1.right=n4;
	n2.left=n5;
	n2.right=n6;
	Demo24 d24 = new Demo24();
	d24.PreorderTravel(root);

}
}

来源：CSDN

作者：meiquanGao

链接：https://blog.csdn.net/qq_43718903/article/details/103617767