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：
public class Solution {
public List<Integer> findMinHeightTrees(int n, int[][] edges) {
List<Integer> leaf=new ArrayList<>();
if(n<=1)
{
leaf.add(0);
return leaf;
}
Map<Integer,List<Integer>> graph=new HashMap<>();
for(int i=0;i<n;i++)
graph.put(i,new ArrayList());
int[] neighbors=new int[n];
for(int[] edge:edges)
{
neighbors[edge[0]]++;
neighbors[edge[1]]++;
graph.get(edge[0]).add(edge[1]);
graph.get(edge[1]).add(edge[0]);
}
for(int i=0;i<n;i++)
{
if(graph.get(i).size()==1)
leaf.add(i);
}
while(n>2)
{
List<Integer> newleaf=new ArrayList<>();
for(int l:leaf)
{
n--;
for(int nb:graph.get(l))
{
if(--neighbors[nb]==1)
newleaf.add(nb);
}
}
leaf=newleaf;
}
return leaf;
}
}