Diameter of Binary Tree

[huimeich]

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.

[huimeich]

def diameterOfBinaryTree(self, root: TreeNode) -> int:
    self.ans = 0
    if not root: return self.ans
    def helper(node: TreeNode) -> int:
        if not node: return 0
        left = helper(node.left)
        right = helper(node.right)
        self.ans = max(self.ans, left + right)
        return max(left, right) + 1
    helper(root)
    return self.ans