From 344b133c095af837d8ac851cce1a552ce08239f5 Mon Sep 17 00:00:00 2001
From: Shivesh Pandey <53203340+pshivesh8@users.noreply.github.com>
Date: Mon, 18 Oct 2021 15:13:14 +0530
Subject: [PATCH] Added Kosaraju Algorithm

---
 DSA/Cpp/Graphs/Kosaraju_Algo.cpp | 86 ++++++++++++++++++++++++++++++++
 1 file changed, 86 insertions(+)
 create mode 100644 DSA/Cpp/Graphs/Kosaraju_Algo.cpp

diff --git a/DSA/Cpp/Graphs/Kosaraju_Algo.cpp b/DSA/Cpp/Graphs/Kosaraju_Algo.cpp
new file mode 100644
index 0000000..64fb098
--- /dev/null
+++ b/DSA/Cpp/Graphs/Kosaraju_Algo.cpp
@@ -0,0 +1,86 @@
+#include<bits/stdc++.h>
+using namespace std;
+
+class Solution
+{
+	public:
+	//Function to find number of strongly connected components in the graph.
+    void dfs(int u, bool vis[], stack<int> &s, vector<int> adj[]) {
+      vis[u] = true;
+      for(auto v: adj[u]) {
+        if(!vis[v]) {
+          dfs(v, vis, s, adj);
+        }
+     }
+    s.push(u);
+    }
+
+  void revDfs(int u, bool vis[], vector<int> adj[]) {
+    vis[u] = true;
+    for(auto v: adj[u]) {
+      if(!vis[v]) {
+        revDfs(v, vis, adj);
+      }
+    }
+  }
+
+  int kosaraju(int V, vector<int> adj[]) {
+    bool vis[V] = {false};
+    stack<int> s;
+
+    for(int i = 0; i < V; i++) { // sort dfs according to finish time
+      if(!vis[i]) {
+        dfs(i, vis, s, adj);
+      }
+    }
+
+    vector<int> tg[V];
+
+    for(int i = 0; i < V; i++) { // transpose the graph(revese all directions)
+      for(auto x : adj[i]) {
+        tg[x].push_back(i);
+        }
+     }
+
+    memset(vis, false, sizeof vis);
+
+    int comp = 0;
+
+    while(!s.empty()) {// tranverse the transposed graph and count components
+      int x = s.top();
+      s.pop();
+      if(!vis[x]) {
+        comp++;
+        revDfs(x, vis, tg);
+      }
+    }
+
+  return comp;
+  }
+};
+
+int main()
+{
+    
+    int t;
+    cin >> t;
+    while(t--)
+    {
+    	int V, E;
+    	cin >> V >> E;
+
+    	vector<int> adj[V];
+
+    	for(int i = 0; i < E; i++)
+    	{
+    		int u, v;
+    		cin >> u >> v;
+    		adj[u].push_back(v);
+    	}
+
+    	Solution obj;
+    	cout << obj.kosaraju(V, adj) << "\n";
+    }
+
+    return 0;
+}