diameter-of-binary-tree.py

# 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 dfs(node):
            if not node:
                return 0
            left = dfs(node.left)
            right = dfs(node.right)
            self.ans = max(self.ans, left + right + 1)
            return max(left, right) + 1

        dfs(root)
        return self.ans - 1