added Kosaraju’s Algorithm for Strongly Connected Components(SCC)

Author: sourav-naskar

CPP/graph_tree/Kosaraju_Algorithm.cpp

@@ -0,0 +1,77 @@
+#include <bits/stdc++.h>
+using namespace std;
+void dfs(int node, stack<int> &st, vector<int> &vis, vector<int> adj[]) {
+    vis[node] = 1; 
+    for(auto it: adj[node]) {
+        if(!vis[it]) {
+            dfs(it, st, vis, adj); 
+        }
+    }
+    
+    st.push(node); 
+}
+void revDfs(int node, vector<int> &vis, vector<int> transpose[]) {
+    cout << node << " "; 
+    vis[node] = 1; 
+    for(auto it: transpose[node]) {
+        if(!vis[it]) {
+            revDfs(it, vis, transpose); 
+        }
+    }
+}
+int main() {
+    int n=6, m=7;
+	vector<int> adj[n+1]; 
+	adj[1].push_back(3);
+	adj[2].push_back(1);
+	adj[3].push_back(2);
+	adj[3].push_back(5);
+	adj[4].push_back(6);
+	adj[5].push_back(4);
+	adj[6].push_back(5);
+	
+	stack<int> st;
+	vector<int> vis(n+1, 0); 
+	for(int i = 1;i<=n;i++) {
+	    if(!vis[i]) {
+	        dfs(i, st, vis, adj); 
+	    }
+	} 
+	
+	vector<int> transpose[n+1]; 
+	
+	for(int i = 1;i<=n;i++) {
+	    vis[i] = 0; 
+	    for(auto it: adj[i]) {
+	        transpose[it].push_back(i); 
+	    }
+	}
+	
+	
+	
+	while(!st.empty()) {
+	    int node = st.top();
+	    st.pop(); 
+	    if(!vis[node]) {
+	        cout << "SCC: "; 
+	        revDfs(node, vis, transpose); 
+	        cout << endl; 
+	    }
+	}
+	
+	
+	return 0;
+}
+
+/*
+Output:
+
+SCC: 1 2 3
+SCC: 5 6 4
+
+Time Complexity: O(N+E), DFS+TopoSort
+
+Space Complexity: O(N+E), Transposing the graph
+*/
+
+//contributed by Sourav Naskar