Leetcode——99. 恢复二叉搜索树

99. 恢复二叉搜索树

二叉搜索树中的两个节点被错误地交换。

请在不改变其结构的情况下，恢复这棵树。

示例 1:

输入: [1,3,null,null,2]

  1
 /
3
 \
  2

输出: [3,1,null,null,2]

  3
 /
1
 \
  2

示例 2:

输入: [3,1,4,null,null,2]

  3
 / \
1   4
   /
  2

输出: [2,1,4,null,null,3]

  2
 / \
1   4
   /
  3

代码：

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {

    private TreeNode pre = null;
    private TreeNode mistake1,mistake2 = null;

    public void recoverTree(TreeNode root) {
        inOrderTraversal(root);
        int temp = mistake2.val;
        mistake2.val = mistake1.val;
        mistake1.val = temp;
    }

    public void inOrderTraversal(TreeNode root){
        if(root == null)
            return;

        inOrderTraversal(root.left);   

        if(pre != null && pre.val > root.val){
            if(mistake1 == null)
            mistake1 = pre;
            mistake2 = root;
        }
        pre = root;
        inOrderTraversal(root.right);
    }
}