# LeetCode – Minimum Height Trees (Java)

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.

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 
```

Java Solution

```public List<Integer> findMinHeightTrees(int n, int[][] edges) { List<Integer> result = new ArrayList<Integer>(); if(n==0){ return result; } if(n==1){ result.add(0); return result; }   ArrayList<HashSet<Integer>> graph = new ArrayList<HashSet<Integer>>(); for(int i=0; i<n; i++){ graph.add(new HashSet<Integer>()); }   for(int[] edge: edges){ graph.get(edge).add(edge); graph.get(edge).add(edge); }   LinkedList<Integer> leaves = new LinkedList<Integer>(); for(int i=0; i<n; i++){ if(graph.get(i).size()==1){ leaves.offer(i); } }   if(leaves.size()==0){ return result; }   while(n>2){ n = n-leaves.size();   LinkedList<Integer> newLeaves = new LinkedList<Integer>();   for(int l: leaves){ int neighbor = graph.get(l).iterator().next(); graph.get(neighbor).remove(l); if(graph.get(neighbor).size()==1){ newLeaves.add(neighbor); } }   leaves = newLeaves; }   return leaves; }```
Category >> Algorithms
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