leetcode-310. Minimum Height Trees

考察点：图，遍历，bfs，路径；
思路：这个题就是从叶子节点开始遍历，去除掉当前所有的叶子节点后，再从新图的叶子节点开始遍历，直到最后剩下一个或者两个叶子节点，就是最深的那个点。

C++ 代码：

class Solution {public:    vector<int> findMinHeightTrees(int n, vector<pair<int, int>>& edges) {        unordered_map<int, unordered_set<int>> mp;        vector<int> leaves;        if (n == 1) {            leaves.push_back(0);            return leaves;        }        for (auto &item : edges) {            mp[item.first].insert(item.second);            mp[item.second].insert(item.first);        }        queue<int> q;        int level[n];        for (int i=0; i<n; i++) {            if (mp[i].size() == 1) {                leaves.push_back(i);            }        }        while (n > 2) {            n -= leaves.size();            vector<int> nextleaves;            for (int i=0; i<leaves.size(); i++) {                int nextNode = *(mp[leaves[i]].begin());                mp[leaves[i]].erase(nextNode);                mp[nextNode].erase(leaves[i]);                if (mp[nextNode].size() == 1) {                    nextleaves.push_back(nextNode);                }            }            leaves = nextleaves;        }        return leaves;    }};