【LeetCode】 Recover Binary Search Tree BST 中序遍历

题目：Recover Binary Search Tree

<span style="font-size:18px;">/* * LeetCode: recover the binary search tree * 题目：二叉树中有两个节点被交换了位置，找出它们，并且将它们换回来，要求用o(n)的连续空间 * 知识点：1、BST树的特点：中序遍历后的节点的排列是按照非降的顺序 * 思路：按照特点中序遍历，当遇到逆序的节点则按照保存相关节点，注意分为，交换的两个点是否相邻的两种情况 */package javaTrain;public class Train6 {public TreeNode firstNode = null,preNode = null,secondNode = null;public int preVal = Integer.MIN_VALUE;    public void recoverTree(TreeNode root) {        if(root == null) return;         findInChild(root);                   int temp = firstNode.val;       firstNode.val = secondNode.val;       secondNode.val = temp;         return;    }    private void findInChild(TreeNode root){    if(root == null) return;    findInChild(root.left);    if(root.val < preVal){    if(firstNode == null){    firstNode = preNode;    secondNode = root;    }    else{    secondNode = root;    return;    }    }    preNode = root;    preVal = root.val;    findInChild(root.right);    }}  </span>