Leetcode-Easy 543. Diameter of Binary Tree

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class Solution:
    def diameterOfBinaryTree(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        self.ans=1
        def depth(node):
            if not node:return 0
            L=depth(node.left)
            R=depth(node.right)
            self.ans=max(self.ans,L+R+1)
            return max(L,R)+1
        depth(root)
        return self.ans-1