543. Diameter of Binary Tree - LeetCode Solution

# 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.ans = 0
        
        def trav(root):
            if not root:
                return 0
            
            left = trav(root.right)
            right = trav(root.left)
            self.ans = max(self.ans,  left+right)
            return 1 + max(left, right)
        
        trav(root)
        return self.ans