[leetcode]99. Recover Binary Search Tree@Java解题报告

https://leetcode.com/problems/recover-binary-search-tree/description/

Two elements of a binary search tree (BST) are swapped by mistake.

Recover the tree without changing its structure.

Note:
A solution using O(n) space is pretty straight forward. Could you devise a constant space solution?

package go.jacob.day805;public class Demo2 {//firstElem第一个被交换的element，secondElem被交换的elementTreeNode firstElem = null, secondElem = null;//把上一个节点初始化为最小值TreeNode preElem = new TreeNode(Integer.MIN_VALUE);public void recoverTree(TreeNode root) {// 中序遍历inOrderTraverse(root);int tmp = firstElem.val;firstElem.val = secondElem.val;secondElem.val = tmp;}private void inOrderTraverse(TreeNode root) {if (root == null)return;inOrderTraverse(root.left);// 1234567到1264537if (firstElem == null && preElem.val >= root.val) {firstElem = preElem;}if (firstElem != null && preElem.val >= root.val) {secondElem = root;}preElem = root;inOrderTraverse(root.right);}private class TreeNode {int val;TreeNode left;TreeNode right;TreeNode(int x) {val = x;}}}