kosajaru.cpp

#include <iostream>
using namespace std;




class Solution
{
private:
    void dfs(int node, vector<int> &vis, vector<int> adj[],
             stack<int> &st) {
        vis[node] = 1;
        for (auto it : adj[node]) {
            if (!vis[it]) {
                dfs(it, vis, adj, st);
            }
        }

        st.push(node);
    }
private:
    void dfs3(int node, vector<int> &vis, vector<int> adjT[]) {
        vis[node] = 1;
        for (auto it : adjT[node]) {
            if (!vis[it]) {
                dfs3(it, vis, adjT);
            }
        }
    }
public:
    //Function to find number of strongly connected components in the graph.
    int kosaraju(int V, vector<int> adj[])
    {
        vector<int> vis(V, 0);
        stack<int> st;
        for (int i = 0; i < V; i++) {
            if (!vis[i]) {
                dfs(i, vis, adj, st);
            }
        }

        vector<int> adjT[V];
        for (int i = 0; i < V; i++) {
            vis[i] = 0;
            for (auto it : adj[i]) {
                // i -> it
                // it -> i
                adjT[it].push_back(i);
            }
        }
        int scc = 0;
        while (!st.empty()) {
            int node = st.top();
            st.pop();
            if (!vis[node]) {
                scc++;
                dfs3(node, vis, adjT);
            }
        }
        return scc;
    }
};

int main() {

    int n = 5;
    int edges[5][2] = {
        {1, 0}, {0, 2},
        {2, 1}, {0, 3},
        {3, 4}
    };
    vector<int> adj[n];
    for (int i = 0; i < n; i++) {
        adj[edges[i][0]].push_back(edges[i][1]);
    }
    Solution obj;
    int ans = obj.kosaraju(n, adj);
    cout << "The number of strongly connected components is: " << ans << endl;
    return 0;
}