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.
* class TreeNode {
* public $val = null;
* public $left = null;
* public $right = null;
* function __construct($val = 0, $left = null, $right = null) {
* $this->val = $val;
* $this->left = $left;
* $this->right = $right;
* }
* }
*/
class Solution {
private $diameter;
/**
* @param TreeNode $root
* @return Integer
*/
public function diameterOfBinaryTree($root) {
$this->diameter = 0;
$this->diameterOfBinaryTreeUtil($root);
return $this->diameter;
}
private function diameterOfBinaryTreeUtil($root) {
if ($root == null) {
return 0;
}
$leftLength = $root->left != null ? 1 + $this->diameterOfBinaryTreeUtil($root->left) : 0;
$rightLength = $root->right != null ? 1 + $this->diameterOfBinaryTreeUtil($root->right) : 0;
$this->diameter = max($this->diameter, $leftLength + $rightLength);
return max($leftLength, $rightLength);
}
}