783. Minimum Distance Between BST Node

方法一，非递归方法，中序遍历

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 
11 static int wing=[]()
12 {
13     std::ios::sync_with_stdio(false);
14     cin.tie(NULL);
15     return 0;
16 }();
17 
18 class Solution 
19 {
20 public:
21     
22     int minDiffInBST(TreeNode* root) 
23     {
24         stack<TreeNode*>s;
25         int mindiff=INT_MAX;
26         TreeNode *p=root;
27         int pre=-(root->val),cur=0;
28         while(p||!s.empty())
29         {
30             if(p)
31             {
32                 s.push(p);
33                 p=p->left;
34             }
35             else
36             {
37                 p=s.top();
38                 s.pop();
39                 cur=p->val;
40                 mindiff=min(mindiff,cur-pre);
41                 pre=cur;
42                 p=p->right;
43             }
44         }
45         return mindiff;
46     }
47 };

方法二，递归方法，中序遍历

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 
11 static int wing=[]()
12 {
13     std::ios::sync_with_stdio(false);
14     cin.tie(NULL);
15     return 0;
16 }();
17 
18 class Solution {
19     int dif=INT_MAX, val=-1;
20 public:
21     int minDiffInBST(TreeNode* root)    
22  {
23         if(root->left!=nullptr) 
24             minDiffInBST(root->left);
25         if(val>=0) dif=min(dif,root->val-val);
26             val=root->val;
27         if(root->right!=nullptr)
28             minDiffInBST(root->right);
29         return dif;
30     }
31     
32 };

简单，问题不大