Diameter of an Undirected Tree

# Diameter of an Undirected Tree Implement `tree_diameter(n: int, edges: list[list[int]]) -> int`. The graph has nodes labeled from `0` through `n - 1`. `edges` describes an undirected connected acyclic graph. Return the diameter: the maximum number of edges on a simple path between any two nodes. ### Input Domain - `1 <= n <= 200,000`. - `len(edges) = n - 1`. - Every edge is `[u, v]` with distinct valid node labels. - The edges form one tree and contain no duplicates. ### Output Rules - Return `0` when `n = 1`. - Measure path length in edges, not nodes. - Return one integer; if several paths attain the diameter, no endpoint tie-break is needed. ### Constraints - Target time is `O(n)`. - Target additional space is `O(n)`. ### Examples #### Example 1 Input: `n = 4, edges = [[0,1],[1,2],[1,3]]` Output: `2` #### Example 2 Input: `n = 1, edges = []` Output: `0` ```hint Use an extreme endpoint Starting from any node, a farthest reachable node can serve as one endpoint of a diameter. ```