**Solution**

**Minimum Absolute Difference in BST** https://leetcode.com/problems/minimum-absolute-difference-in-bst/?tab=Description

**Inorder Traversal**

- Simple in-order traversal to track MAD.

```
class Solution(object):
def in_order(self, root):
if root == None:
return
self.in_order(root.left)
if self.prev is not None:
self.min_abs = min(self.min_abs, abs(root.val-self.prev))
self.prev = root.val
self.in_order(root.right)
return
def getMinimumDifference(self, root):
"""
:type root: TreeNode
:rtype: int
"""
self.prev, self.min_abs = None, float('inf')
self.in_order(root)
return self.min_abs
```