python中序遍历

class Solution:
# 返回对应节点TreeNode

def KthNode(self, pRoot, k):
    # write code here
    self.k = k
    self.res = None
    def helper(node):
        if not node:
            return

        if node.left:
            helper(node.left)

        if self.k == 1:
            self.res = node
        self.k -= 1

        if node.right:
            helper(node.right)
    helper(pRoot)
    return self.res