543. Diameter of Binary Tree

JIAKAOBO

LeetCode

感谢赞助!

• ㊗️
• 大家
• offer
• 多多！

Problem

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: 3is 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, 10^4].
• -100 <= Node.val <= 100

Code

class Solution {
    int max = 0;
    
    public int diameterOfBinaryTree(TreeNode root) {
        helper(root);
        return max;
    }

    private int helper(TreeNode root) {
        if (root == null) return 0;
        
        int left = helper(root.left);
        int right = helper(root.right);
        
        max = Math.max(max, left + right);
        
        return Math.max(left, right) + 1;
    }
}

class Solution {
    public int diameterOfBinaryTree(TreeNode root) {
        if (root == null) return 0;
        
        int left = getHeight(root.left);
        int right = getHeight(root.right);
        
        int leftMax = diameterOfBinaryTree(root.left);
        int rightMax = diameterOfBinaryTree(root.right);
        

        return Math.max((left + right), Math.max(leftMax, rightMax));
    }

    private int getHeight(TreeNode root) {
        if (root == null) return 0;

        return 1 + Math.max(getHeight(root.left), getHeight(root.right));
    }
}