783. Minimum Distance Between BST Node

方法一，非递归方法，中序遍历

 /**
  * Definition for a binary tree node.
  * struct TreeNode {
  *     int val;
  *     TreeNode *left;
  *     TreeNode *right;
  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
  * };
  */

 static int wing=[]()
 {
     std::ios::sync_with_stdio(false);
     cin.tie(NULL);
     return ;
 }();

 class Solution
 {
 public:

     int minDiffInBST(TreeNode* root)
     {
         stack<TreeNode*>s;
         int mindiff=INT_MAX;
         TreeNode *p=root;
         int pre=-(root->val),cur=;
         while(p||!s.empty())
         {
             if(p)
             {
                 s.push(p);
                 p=p->left;
             }
             else
             {
                 p=s.top();
                 s.pop();
                 cur=p->val;
                 mindiff=min(mindiff,cur-pre);
                 pre=cur;
                 p=p->right;
             }
         }
         return mindiff;
     }
 };

方法二，递归方法，中序遍历

 /**
  * Definition for a binary tree node.
  * struct TreeNode {
  *     int val;
  *     TreeNode *left;
  *     TreeNode *right;
  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
  * };
  */

 static int wing=[]()
 {
     std::ios::sync_with_stdio(false);
     cin.tie(NULL);
     return ;
 }();

 class Solution {
     int dif=INT_MAX, val=-;
 public:
     int minDiffInBST(TreeNode* root)
  {
         if(root->left!=nullptr)
             minDiffInBST(root->left);
         if(val>=) dif=min(dif,root->val-val);
             val=root->val;
         if(root->right!=nullptr)
             minDiffInBST(root->right);
         return dif;
     }

 };

简单，问题不大