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leetcode310.java
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leetcode310.java
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public class Solution {
public List<Integer> findMinHeightTrees(int n, int[][] edges) {
if(n == 1){
return Collections.singletonList(0);
}
// use for storing adj table
Map<Integer, Set<Integer>> adj = new HashMap<>();
for(int i = 0; i < n; i++){
adj.put(i,new HashSet<Integer>());
}
// store adj table
for(int[] edge : edges){
adj.get(edge[0]).add(edge[1]);
adj.get(edge[1]).add(edge[0]);
}
List<Integer> leaves = new ArrayList<>();
for(int i = 0; i < n; i++){
if(adj.get(i).size() == 1){
leaves.add(i);
}
}
while(n > 2){
n -= leaves.size();
List<Integer> newLeaves = new ArrayList<>();
for(int leaf : leaves){
for(int newleaf : adj.get(leaf)){
adj.get(leaf).remove(newleaf);
adj.get(newleaf).remove(leaf);
if(adj.get(newleaf).size() == 1){
newLeaves.add(newleaf);
}
}
}
leaves = newLeaves;
}
return leaves;
}
}