# 310 Minimum Height Trees

## 1. Question

For a undirected graph with tree characteristics, we can choose any node as the root. The result graph is then a rooted tree. Among all possible rooted trees, those with minimum height are called minimum height trees (MHTs). Given such a graph, write a function to find all the MHTs and return a list of their root labels.
Format The graph contains`n`nodes which are labeled from`0`to`n - 1`. You will be given the number`n`and a list of undirected`edges`(each edge is a pair of labels).
You can assume that no duplicate edges will appear in`edges`. Since all edges are undirected,`[0, 1]`is the same as`[1, 0]`and thus will not appear together in`edges`.
Example 1:
Given`n = 4`,`edges = [[1, 0], [1, 2], [1, 3]]`
0
|
1
/ \
2 3
return``
Example 2:
Given`n = 6`,`edges = [[0, 3], [1, 3], [2, 3], [4, 3], [5, 4]]`
0 1 2
\ | /
3
|
4
|
5
return`[3, 4]`
Note:
(1) According to the definition of tree on Wikipedia: “a tree is an undirected graph in which any two vertices are connected byexactlyone path. In other words, any connected graph without simple cycles is a tree.”
(2) The height of a rooted tree is the number of edges on the longest downward path between the root and a leaf.

## 2. Implementation

(1) BFS
class Solution {
public List<Integer> findMinHeightTrees(int n, int[][] edges) {
List<Integer> res = new ArrayList<>();
if (n == 1) {
return res;
}
for (int i = 0; i < n; i++) {
}
for (int[] edge : edges) {
}
List<Integer> leaves = new ArrayList<>();
List<Integer> newLeaves = null;
for (int i = 0; i < n; i++) {
}
}
while (n > 2) {
n -= leaves.size();
newLeaves = new ArrayList<>();
for (int node : leaves) {
for (int parent : adjList.get(node)) {