LeetCode 99. Recover Binary Search Tree(BST，中序遍历)

c++
 ```
 /**
Definition for a binary tree node.
struct TreeNode {
int val;
TreeNode *left;
TreeNode *right;
TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};
 */
 class Solution {
 public:
 TreeNode* last;
 TreeNode* pre;
 int tag=0;
 int ans=0;
 int m = -123987523;
 void recoverTree(TreeNode* root) {
  if(root==NULL)      return;   last = new TreeNode(m);   fun(root);   if(ans==0)  {      int temp = pre->val;      pre->val = last->val;      last->val = temp;  }
 }
 void fun(TreeNode* root)
 {
 if(root->left!=NULL)
 {
 fun(root->left);
 }
  if(last->val == m )  {      last=root;  }  else if(last->val<root->val)  {      if(tag==1)      {          int temp = pre->val;          pre->val = last->val;          last->val = temp;          ans=1;      }      last=root;      tag=0;  }  else  {      tag=1;  }   pre=root;   if(root->right!=NULL)  {      fun(root->right);  }
 }
 };
 ```