TheAlgorithms-C-Plus-Plus/graph/connected_components.cpp

#include <iostream>
#include <vector>

using std::vector;

class graph
{
 private:
    vector<vector<int>> adj;
    int connected_components;
    void depth_first_search();
    void explore(int, vector<bool> &);

 public:
    explicit graph(int n) : adj(n, vector<int>()) { connected_components = 0; }
    void addEdge(int, int);
    int getConnectedComponents()
    {
        depth_first_search();
        return connected_components;
    }
};

void graph::addEdge(int u, int v)
{
    adj[u - 1].push_back(v - 1);
    adj[v - 1].push_back(u - 1);
}

void graph::depth_first_search()
{
    int n = adj.size();
    vector<bool> visited(n, false);

    for (int i = 0; i < n; i++)
    {
        if (!visited[i])
        {
            explore(i, visited);
            connected_components++;
        }
    }
}

void graph::explore(int u, vector<bool> &visited)
{
    visited[u] = true;
    for (auto v : adj[u])
    {
        if (!visited[v])
        {
            explore(v, visited);
        }
    }
}

int main()
{
    graph g(4);
    g.addEdge(1, 2);
    g.addEdge(3, 2);
    std::cout << g.getConnectedComponents();
    return 0;
}