剑指offer【55】求二叉树的深度

先序遍历解法：

class BintNode:
    def __init__(self,data,left=None,right=None):
        self.data=data
        self.left=left
        self.right=right


class Solution:
    
    def depth(self,tree):
        
        if tree == None:
            return 0
        
        depth(tree.left)
        depth(tree.right)

        return max(depth(tree.left),depth(tree.right))+1