[leetcode] 543. Diameter of Binary Tree

Given the root of a binary tree, return 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 a path between two nodes is represented by the number of edges between them.

 

Example 1:

Input: root = [1,2,3,4,5]
Output: 3
Explanation: 3 is the length of the path [4,2,1,3] or [5,2,1,3].

Example 2:

Input: root = [1,2]
Output: 1

 

Constraints:

• The number of nodes in the tree is in the range [1, 104].
• -100 <= Node.val <= 100

 

 

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):
    longest = 0
    def diameterOfBinaryTree(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        def dfs(node):
            if not node:
                return -1 
            left = dfs(node.left)
            right = dfs(node.right)

            self.longest = max(self.longest, left + right + 2)
            return max(left, right) +1 

        dfs(root)
        return self.longest