1class TreeNode:
2    def __init__(self, val=0, left=None, right=None):
3        self.val = val
4        self.left = left
5        self.right = right
6
7class Solution:
8    def minDiffInBST(self, root: TreeNode) -> int:
9        stack, prev_value, min_diff = [], None, float('inf')
10        current = root
11        
12        while stack or current:
13            while current:
14                stack.append(current)
15                current = current.left
16            current = stack.pop()
17            if prev_value is not None:
18                min_diff = min(min_diff, current.val - prev_value)
19            prev_value = current.val
20            current = current.right
21
22        return min_diff
23

1#include<limits>
using namespace std;

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 {
    int minDiff = numeric_limits<int>::max();
    int prevValue = -1;
public:
    void inOrder(TreeNode* node) {
        if (node == nullptr) return;
        inOrder(node->left);
        if (prevValue >= 0) {
            minDiff = min(minDiff, node->val - prevValue);
        }
        prevValue = node->val;
        inOrder(node->right);
    }

    int minDiffInBST(TreeNode* root) {
        prevValue = -1;
        minDiff = numeric_limits<int>::max();
        inOrder(root);
        return minDiff;
    }
};