1245. Tree Diameter

Given an undirected tree, return its diameter: the number of edges in a longest path in that tree.

The tree is given as an array of  edges  where edges[i] = [u, v] is a bidirectional edge between nodes  u and v .  Each node has labels in the set {0, 1, ..., edges.length} .

Example 1:

Input:

 edges = [[0,1],[0,2]]
Output:

 2
Explanation: 

A longest path of the tree is the path 1 - 0 - 2.

Example 2:

Input:

 edges = [[0,1],[1,2],[2,3],[1,4],[4,5]]
Output:

 4
Explanation: 

A longest path of the tree is the path 3 - 2 - 1 - 4 - 5.

Constraints:

• 0 <= edges.length < 10^4
• edges[i][0] != edges[i][1]
• 0 <= edges[i][j] <= edges.length
• The given edges form an undirected tree.

1、题目描述¶

给你这棵「无向树」，请你测算并返回它的「直径」：这棵树上最长简单路径的 边数。

我们用一个由所有「边」组成的数组 edges 来表示一棵无向树，其中 edges[i] = [u, v] 表示节点 u 和 v 之间的双向边。

树上的节点都已经用 {0, 1, ..., edges.length} 中的数做了标记，每个节点上的标记都是独一无二的。

示例 1：

输入：edges = [[0,1],[0,2]]
输出：2
解释：
这棵树上最长的路径是 1 - 0 - 2，边数为 2。

示例 2：

输入：edges = [[0,1],[1,2],[2,3],[1,4],[4,5]]
输出：4
解释： 
这棵树上最长的路径是 3 - 2 - 1 - 4 - 5，边数为 4。

提示：

• $0 <= edges.length < 10^4$
• $edges[i][0] != edges[i][1]$
• $0 <= edges[i][j] <= edges.length$
• edges 会形成一棵无向树