【Leetcode-easy-543】Diameter of Binary Tree

【Leetcode-easy-543】Diameter of Binary Tree

这个是秒针系统的面试题，当时把题目理解错了，面试一个多小时最后挂了。

古有八股，今有Leetcode，加油。

题目

Given a binary tree, you need to compute 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.

Example:

Given a binary tree

1
/ \
2   3
/ \
4   5

Return 3, which is the length of the path [4,2,1,3] or [5,2,1,3].

Note: The length of path between two nodes is represented by the number of edges between them.

思路

对于每一个结点，经过它的最长路径的长度 = 它的左子树的最大深度 + 右子树的最大深度。

程序

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
class Solution {
//     public int diameterOfBinaryTree(TreeNode root) {
//         if (root == null) return 0;
//         int left = depth(root.left);
//         int right = depth(root.right);
//         return left + right;
//     }

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

int max = 0;

public int diameterOfBinaryTree(TreeNode root) {
maxDepth(root);
return max;
}

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