LeetCode-in-All
543. Diameter of Binary Tree
Easy
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
Solution
# Definition for a binary tree node.
#
# defmodule TreeNode do
# @type t :: %__MODULE__{
# val: integer,
# left: TreeNode.t() | nil,
# right: TreeNode.t() | nil
# }
# defstruct val: 0, left: nil, right: nil
# end
defmodule Solution do
@spec diameter_of_binary_tree(root :: TreeNode.t | nil) :: integer
def diameter_of_binary_tree(root),
do: rec_diameter(root)
|> then(fn {max, _} -> max end)
@spec rec_diameter(root :: TreeNode.t | nil) :: {integer, integer}
defp rec_diameter(nil), do: {0, 0}
defp rec_diameter(%TreeNode{left: l, right: r}) do
{l_max, l_longest} = rec_diameter(l)
{r_max, r_longest} = rec_diameter(r)
{max(max(l_max, r_max), l_longest + r_longest), max(l_longest, r_longest) + 1}
end
end