1319

class Solution {
public:
    int makeConnected(int n, vector<vector<int>>& connections) {
        if(connections.size() < n-1) return -1;
        int components = 0;

        vector<vector<int>> g;
        g.resize(n);
        for(auto edge: connections){
            g[edge[0]].push_back(edge[1]);
            g[edge[1]].push_back(edge[0]);
        }

        vector<bool> vis(n, false);
        for(int i=0; i<n; i++)
            if(!vis[i])
                dfs(i, g, vis), components++;
        return components-1;
    }

    void dfs(int node, vector<vector<int>> &g, vector<bool> &vis){
        vis[node] = true;
        for(int child: g[node])
            if(!vis[child])
                dfs(child, g, vis);
    }
};