Diameter of Binary Tree

Question

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.

Tags

• Tree

Thought

Use the recursion to find the depth of the subtree and compare with the maximum diameter.

Code

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def helper(self, node):
        if node is None:
            return 0, 0
        leftDepth, leftDiameter = self.helper(node.left)
        rightDepth, rightDiameter = self.helper(node.right)
        diameter = max([leftDiameter, rightDiameter, leftDepth + rightDepth])
        return max(leftDepth, rightDepth) + 1, diameter



    def diameterOfBinaryTree(self, root):
        """
        Use recursive
        :type root: TreeNode
        :rtype: int
        """
        depth, diameter = self.helper(root)
        return diameter