二叉搜索树与双向链表

题目描述

输入一棵二叉搜索树，将该二叉搜索树转换成一个排序的双向链表。要求不能创建任何新的结点，只能调整树中结点指针的指向。

递归

/**public class TreeNode {    int val = 0;    TreeNode left = null;    TreeNode right = null;    public TreeNode(int val) {        this.val = val;    }}*/public class Solution {    TreeNode head = null;    TreeNode realHead = null;    public TreeNode Convert(TreeNode pRootOfTree) {        ConvertSub(pRootOfTree);        return realHead;    }    public void ConvertSub(TreeNode pRootOfTree) {        if(pRootOfTree==null) return;        ConvertSub(pRootOfTree.left);        if(head == null) {            head = pRootOfTree;            realHead = pRootOfTree;        } else {//把根节点插入到双向链表右边，head向后移动            head.right = pRootOfTree;            pRootOfTree.left = head;            head = pRootOfTree;        }        ConvertSub(pRootOfTree.right);    }}

非递归

/**public class TreeNode {    int val = 0;    TreeNode left = null;    TreeNode right = null;    public TreeNode(int val) {        this.val = val;    }}*/import java.util.Stack;public class Solution {    public TreeNode Convert(TreeNode pRootOfTree) {        if(pRootOfTree == null) return pRootOfTree;        Stack<TreeNode> stack = new Stack<TreeNode>();        TreeNode p = pRootOfTree;        TreeNode pre = null;// 用于保存中序遍历序列的上一节点        Boolean c = true;        while(p!=null || !stack.empty()) {        while(p!=null) {                stack.push(p);                p = p.left;            }            p = stack.pop();            if(c) {                pRootOfTree = p;                pre = pRootOfTree;                c = false;            } else {                pre.right = p;                p.left = pre;                pre = p;            }            p = p.right;        }        return pRootOfTree;            }}