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:

Solution

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public var val: Int
 *     public var left: TreeNode?
 *     public var right: TreeNode?
 *     public init() { self.val = 0; self.left = nil; self.right = nil; }
 *     public init(_ val: Int) { self.val = val; self.left = nil; self.right = nil; }
 *     public init(_ val: Int, _ left: TreeNode?, _ right: TreeNode?) {
 *         self.val = val
 *         self.left = left
 *         self.right = right
 *     }
 * }
 */
class Solution {
    private var diameter: Int = 0

    func diameterOfBinaryTree(_ root: TreeNode?) -> Int {
        diameter = 0
        _ = diameterOfBinaryTreeUtil(root)
        return diameter
    }

    private func diameterOfBinaryTreeUtil(_ root: TreeNode?) -> Int {
        guard let root = root else {
            return 0
        }
        let leftLength = root.left != nil ? 1 + diameterOfBinaryTreeUtil(root.left) : 0
        let rightLength = root.right != nil ? 1 + diameterOfBinaryTreeUtil(root.right) : 0
        diameter = max(diameter, leftLength + rightLength)
        return max(leftLength, rightLength)
    }
}