Solution: Find Minimum Diameter After Merging Two Trees

Explore how to find the minimal diameter when merging two undirected trees by leveraging breadth-first search twice to identify tree diameters. Understand how to build adjacency lists, apply BFS to find farthest nodes, and use a precise formula to connect trees optimally through their centers. This lesson helps develop efficient tree traversal and problem-solving skills applicable to coding interviews and graph algorithms.

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Statement
Solution
- Time complexity
- Space complexity

Statement

You are given two undirected trees: one with $n$ nodes labeled from $0$ to $n - 1$ , and another with $m$ nodes labeled from $0$ to $m - 1$ . Their structures are defined by two $2D$ integer arrays—edges1 of length $n - 1$ for the first tree, and edges2 of length $m - 1$ for the second. Each element edges1[i] = [aᵢ, bᵢ] represents an edge between nodes $aᵢ$ and $bᵢ$ in the first tree, and similarly, edges2[i] = [uᵢ, vᵢ] represents an edge in the second tree.

Your task is to connect any node from the first tree to any one node from the second tree using a single edge. Return the smallest possible diameter of the resulting combined tree.

Note: The diameter of a tree is the length of the longest path between any two nodes in it.

Constraints:

$1 <= n, m <= 10^5$
edges1.length $== n - 1$ ...