1319.cpp

class Solution {
    void dfs(vector<vector<int>> &adj, vector<bool> &visited, int src) {
        visited[src] = true;
        for(int i : adj[src])
            if(!visited[i])
                dfs(adj, visited, i);
    }

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

        vector<vector<int>> adj(n);

        for(auto& v : connections) {
            adj[v[0]].push_back(v[1]);
            adj[v[1]].push_back(v[0]);
        }

        vector<bool> visited(n, false);
        int components = 0;
        
        for(int i = 0; i < n; i++) {
            if(!visited[i]) {
                dfs(adj, visited, i);
                components++;
            }
        }

        return components - 1;
    }
};