530. Minimum Absolute Difference in BST

Python

from math import inf


class Solution:
    def getMinimumDifference(self, root: Optional[TreeNode]) -> int:

        def dfs(node, upper, lower):
            if not node:
                return upper - lower
        
            return min(
                dfs(node.left, node.val, lower),
                dfs(node.right, upper, node.val)
            )
            
        return dfs(root, inf, -inf)