LeetCode "Graph Valid Tree"

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DFS to check cyclic. Please note some details.

class Solution{    unordered_map<int, unordered_set<int>> g;    unordered_set<int> visited;        bool go(int i, int p) // true - cyclic    {        visited.insert(i);        auto &cs = g[i];        for (auto c : cs)        {            if (c == p) continue;            if (visited.find(c) != visited.end()) return true;            bool b = go(c, i);            if (b) return true;        }        return false;    }public:    bool validTree(int n, vector<pair<int, int>>& edges)    {        int vcnt = n - 1;        int ecnt = edges.size();        if (ecnt != vcnt) return false;                //    Build Graphs        for (auto &p : edges)        {            g[p.first].insert(p.second);            g[p.second].insert(p.first);        }        //    DFS        for (int i = 0; i < n; i++)        {            if (visited.find(i) == visited.end())            {                bool ret = go(i, -1);                if (ret)                     return false;            }        }        return true;    }};

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LeetCode "Graph Valid Tree"