DiameterOfBinaryTree.py

class Solution:
   
    def diameterOfBinaryTree(self, root: TreeNode) -> int:
        self.globalLongestPath = 0
        self.depth(root)
        return self.globalLongestPath

    def depth(self, node:TreeNode)-> int:
        if not node:
            return 0
        left = self.depth(node.left)
        right = self.depth(node.right)
        self.globalLongestPath = max(self.globalLongestPath, left + right)
        return max(left,right)+1