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 [1]
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]
借鉴的别人的代码：
1 public class Solution { 2 public List<Integer> findMinHeightTrees(int n, int[][] edges) { 3 4 List<Integer> leaf=new ArrayList<>(); 5 if(n<=1) 6 { 7 leaf.add(0); 8 return leaf; 9 } 10 11 Map<Integer,List<Integer>> graph=new HashMap<>(); 12 for(int i=0;i<n;i++) 13 graph.put(i,new ArrayList()); 14 15 int[] neighbors=new int[n]; 16 for(int[] edge:edges) 17 { 18 neighbors[edge[0]]++; 19 neighbors[edge[1]]++; 20 graph.get(edge[0]).add(edge[1]); 21 graph.get(edge[1]).add(edge[0]); 22 } 23 24 for(int i=0;i<n;i++) 25 { 26 if(graph.get(i).size()==1) 27 leaf.add(i); 28 } 29 30 while(n>2) 31 { 32 List<Integer> newleaf=new ArrayList<>(); 33 for(int l:leaf) 34 { 35 n--; 36 for(int nb:graph.get(l)) 37 { 38 if(--neighbors[nb]==1) 39 newleaf.add(nb); 40 } 41 42 } 43 leaf=newleaf; 44 } 45 return leaf; 46 } 47 }
原文：http://www.cnblogs.com/ghuosaao/p/5435291.html