Minimum Height Trees

A tree is an undirected graph in which any two vertices are connected by exactly one path. In other words, any connected graph without simple cycles is a tree. Given a tree of `n` nodes labelled from `0` to `n - 1`, and an array of `n - 1` `edges` where `edges[i] = [ai, bi]` indicates that there is an undirected edge between the two nodes `ai` and `bi` in the tree, you can choose any node of the tree as the root. When you select a node `x` as the root, the result tree has height `h`. Among all possible rooted trees, those with minimum height (i.e. `min(h)`)  are called **minimum height trees** (MHTs). Return _a list of all **MHTs'** root labels_. You can return the answer in **any order**. The **height** of a rooted tree is the number of edges on the longest downward path between the root and a leaf.   **Example 1:** **Input:** n = 4, edges = [[1,0],[1,2],[1,3]] **Output:** [1] **Explanation:** As shown, the height of the tree is 1 when the root is the node with label 1 which is the only MHT. ``` **Example 2:** **Input:** n = 6, edges = [[3,0],[3,1],[3,2],[3,4],[5,4]] **Output:** [3,4] ```   **Constraints:** - `1 <= n <= 2 * 104` - `edges.length == n - 1` - `0 <= ai, bi < n` - `ai != bi` - All the pairs `(ai, bi)` are distinct. - The given input is **guaranteed** to be a tree and there will be **no repeated** edges.