/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int pre_val = INT_MIN , diff_val = INT_MAX;
    void min_diff(TreeNode* cur)
    {
        if(cur==nullptr) return ;
        min_diff(cur->left);
        if(pre_val != -1 && ( cur->val - pre_val ) < diff_val) diff_val = cur->val - pre_val;
        pre_val = cur->val;
        min_diff(cur->right);
    }
    int getMinimumDifference(TreeNode* root) {
        if(root==nullptr) return 0;
        min_diff(root);
        return diff_val;
    }
};

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    double result = INT_MAX;
    TreeNode* pre = nullptr;
    void trak_back(TreeNode* cur)
    {
        if( cur == nullptr ) return;
        trak_back(cur->left);
        if(pre != nullptr && cur->val - pre->val　< result )
            result =  cur->val - pre->val;
        pre = cur;
        trak_back(cur->right);
    }
    int getMinimumDifference(TreeNode* root) {
        if(root == nullptr) return 0;
        trak_back(root);
        return result;
    }
};