class Solution {
    public List<Integer> findMinHeightTrees(int n, int[][] edges) {
        if(n == 1) {
            return Collections.singletonList(0);
        }
        
        List<Set<Integer>> adjList = new ArrayList<>();
        for(int i = 0; i < n; i++) {
            adjList.add(new HashSet<Integer>());
        }
        for(int[] edge : edges) {
            adjList.get(edge[0]).add(edge[1]);
            adjList.get(edge[1]).add(edge[0]);
        }
        
        List<Integer> leaves = new ArrayList<>();
        for(int i = 0; i < n; i++) {
            if(adjList.get(i).size() == 1) {
                leaves.add(i);
            }
        }
        
        int num;
        while(n > 2) {
            n -= leaves.size();
            List<Integer> newLeaves = new ArrayList<>();
            
            for(int i : leaves) {
                num = adjList.get(i).iterator().next();
                adjList.get(num).remove(i);
                
                if(adjList.get(num).size() == 1) {
                    newLeaves.add(num);
                }
            }
            
            leaves = newLeaves;
        }
        
        return leaves;
    }
}