310. Minimum Height Trees--Find out which nodes in the graph are root and the depth of the tree is minimal

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 is 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 is labeled from 0 to n - 1 . You'll be given the number and n a list of undirected edges (each edge is a pair of labels).

You can assume that no duplicate edges would appear in edges . Since all edges was undirected, is the same as and thus would not [0, 1] [1, 0] 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]

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Note:

(1) According to the definition of the tree on Wikipedia: "A tree was an undirected graph in which any and vertices is connect Ed by exactly one path. In the other words, any connected graph without simple cycles is a tree. "

(2) The height of a rooted tree is the number of edges on the longest downward path between the root and a leaf.

vector<int> Findminheighttrees (intN, vector<pair<int,int>>&edges) {    //Corner Case    if(N <=1)return{0}; //construct a edges search data stucturevector<unordered_set<int>>graph (n);  for(Auto e:edges) {Graph[e.first].insert (E.second);    Graph[e.second].insert (E.first); }            //Find all of the leaf nodesvector<int>Current ;  for(intI=0; I<graph.size (); i++){        if(graph[i].size () = =1) Current.push_back (i); }            //BFS the graph     while(true) {vector<int>Next;  for(intnode:current) {             for(intNeighbor:graph[node])                {graph[neighbor].erase (node); if(graph[neighbor].size () = =1) Next.push_back (neighbor); }        }        if(Next.empty ()) Break; Current=Next; }    returnCurrent ;}

Remove the outermost circle of leaf nodes at a time. The last remaining set of nodes is what is asked.

310. Minimum Height Trees--Find out which nodes in the graph are rooted, and the depth of the tree is minimal