Diameter of Binary Tree

diameter_of_binary_tree.py

"""
Description:
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.
The length of path between two nodes is represented by the number of edges between them.

Example:
Input:
          1
         / \
        2   3
       / \     
      4   5    
Output: 3 -- [4, 2, 1, 3] or [5, 2, 1, 3]
"""

class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

def diameterOfBinaryTree(root):
    """
    :type root: TreeNode
    :rtype: int
    """
    def walk(root):
        if not root:
            return 0, 0
        else:
            l_depth, l_diam = walk(root.left)
            r_depth, r_diam = walk(root.right)
            depth = max(l_depth, r_depth) + 1
            diam = max(l_depth + r_depth, l_diam, r_diam)
            return depth, diam
    _, diameter = walk(root)
    return diameter