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.
#|
; val : integer?
; left : (or/c tree-node? #f)
; right : (or/c tree-node? #f)
(struct tree-node
(val left right) #:mutable #:transparent)
; constructor
(define (make-tree-node [val 0])
(tree-node val #f #f))
|#
(define/contract (diameter-of-binary-tree root)
(-> (or/c tree-node? #f) exact-integer?)
; Use let/cc to simulate a mutable variable for diameter
(let/cc return
(let ([diameter 0])
; Helper function that both updates max diameter and returns height
(define (diameter-helper node)
(if (not node)
0
(let* ([left-len (if (tree-node-left node)
(add1 (diameter-helper (tree-node-left node)))
0)]
[right-len (if (tree-node-right node)
(add1 (diameter-helper (tree-node-right node)))
0)])
; Update diameter if current path is longer
(set! diameter (max diameter (+ left-len right-len)))
; Return max height of this subtree
(max left-len right-len))))
; Call helper function and return final diameter
(diameter-helper root)
diameter)))