Leetcode 783. 二叉搜索树结点最小距离

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def minDiffInBST(self, root: TreeNode) -> int:
        self.lastVal,self.ret=None,None
        def inOrderTraversal(node):
            if node:
                inOrderTraversal(node.left)
                if self.ret!=None:
                    self.ret=min(self.ret,node.val-self.lastVal)
                elif self.lastVal!=None:
                    self.ret=node.val-self.lastVal
                self.lastVal=node.val
                inOrderTraversal(node.right)
        inOrderTraversal(root)
        return self.ret