0543-Diameter-of-Binary-Tree.py

'''
Given a binary tree, you need to compute the length of the diameter of the tree. The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root.

Example:
Given a binary tree
          1
         / \
        2   3
       / \
      4   5
Return 3, which is the length of the path [4,2,1,3] or [5,2,1,3].

Note: The length of path between two nodes is represented by the number of edges between them.
'''
# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def diameterOfBinaryTree(self, root: TreeNode) -> int:
        self.diameter = 0
        def depth(root):
            if not root:
                return 0
            l = depth(root.left)
            r = depth(root.right)
            self.diameter = max(self.diameter, l+r)
            return max(l,r)+1
        depth(root)
        return self.diameter