問題
A tree is a connected undirected graph with no cycles. Its diameter is the largest number of edges on a path between any two vertices. Return that length; you do not need to return the path. No root is specified.
Implement tree_diameter(vertices, edges).
Input
vertices: The number of vertices.
edges: Undirected connections [u, v].
Output
Return the diameter measured in edges, not vertices.
制約
1 ≤ vertices ≤ 200,000. Exactly vertices − 1 edges, with distinct endpoints in 1…vertices. Inputs always form a tree. A one-vertex tree has diameter 0.
例
例 1
入力：
edges = [
[1, 2],
[2, 3],
[3, 4],
[2, 5]
]
vertices = 5
期待される出力：
expected = 3入力：
std::vector<std::vector<long long>> edges = {
{1, 2},
{2, 3},
{3, 4},
{2, 5}
};
long long vertices = 5;
期待される出力：
long long expected = 3;入力：
long[][] edges = new long[][] {
new long[] {1, 2},
new long[] {2, 3},
new long[] {3, 4},
new long[] {2, 5}
};
long vertices = 5;
期待される出力：
long expected = 3;解説
The path 5–2–3–4 contains three edges. No path in this tree is longer.
例 2
入力：
edges = []
vertices = 1
期待される出力：
expected = 0入力：
std::vector<std::vector<long long>> edges = {};
long long vertices = 1;
期待される出力：
long long expected = 0;入力：
long[][] edges = new long[][] {};
long vertices = 1;
期待される出力：
long expected = 0;解説
A single vertex has no edges, so the longest path length is 0.
参考資料
この課題はCodeUtility用に調整されています。上記の説明と制約に従ってください。