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
     
      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             else36             {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