60.py

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def getMinimumDifference(self, root: Optional[TreeNode]) -> int:
        node_values = []

        def dfs(node):
            if node is None:
                return

            node_values.append(node.val)
            dfs(node.left)
            dfs(node.right)

        dfs(root)

        node_values.sort()
        min_diff = 1e9
        for i in range(1, len(node_values)):
            min_diff = min(min_diff, node_values[i] - node_values[i - 1])

        return min_diff