刷题感悟

将二叉查找树转化成双向链表

题目思路其实不难 ，中序遍历，然后再依次的将数据放入链表中即可

重点：新加元素前后链的配置 

有个有意思的地方在于result没有赋初值 导致写代码时需要先初始化 然后删除之 。

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 * Definition for Doubly-ListNode.
 * public class DoublyListNode {
 *     int val;
 *     DoublyListNode next, prev;
 *     DoublyListNode(int val) {
 *         this.val = val;
 *         this.next = this.prev = null;
 *     }
 * }
 */ 
public class Solution {
    /**
     * @param root: The root of tree
     * @return: the head of doubly list node
     */
    public DoublyListNode bstToDoublyList(TreeNode root) {  
        // Write your code here
        if(root==null)return null;
        DoublyListNode rootsult = new DoublyListNode(0);
        midOrder(root,rootsult);
        rootsult = rootsult.next;
        return rootsult;
    }
    
    public void midOrder(TreeNode root,DoublyListNode result){
        if(root.left!=null)midOrder(root.left,result);
        setNode(root.val, result);
        if(root.right!=null)midOrder(root.right,result);
    }
    public void setNode(int val,DoublyListNode result){
        if(result==null) result = new DoublyListNode(val);
        else{
            DoublyListNode node = new DoublyListNode(val);
            while(result.next!=null)result = result.next;
            node.prev=result;
            result.next = node;
        }
    }
}

在大数据量的情况下 有可能会爆栈

下一步想想如何用非递归的方法实现之 占坑