From 5da2760d3fba77d88a98c0ad3e61bb13ad639777 Mon Sep 17 00:00:00 2001
From: Anirban Chetia <bloodraven166@gmail.com>
Date: Mon, 18 Nov 2019 20:16:58 +0530
Subject: [PATCH 1/4] Kosaraju Algorithm for SCCs.

---
 Graph/Kosaraju.cpp | 103 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 103 insertions(+)
 create mode 100644 Graph/Kosaraju.cpp

diff --git a/Graph/Kosaraju.cpp b/Graph/Kosaraju.cpp
new file mode 100644
index 000000000..a9131faa8
--- /dev/null
+++ b/Graph/Kosaraju.cpp
@@ -0,0 +1,103 @@
+/* Implementation of Kosaraju's Algorithm to find out the strongly connected components (SCCs) in a graph. 
+   Author:Anirban166
+*/
+
+#include<iostream>
+#include<vector>
+
+using namespace std;
+
+void print(vector<int> a[],int V)
+{
+    for(int i=0;i<V;i++)
+    {
+        if(!a[i].empty())
+            cout<<"i="<<i<<"-->";
+        for(int j=0;j<a[i].size();j++)
+            cout<<a[i][j]<<" ";
+        if(!a[i].empty())
+            cout<<endl;
+    }
+}
+void calculate_time(int v,stack<int> &st,bool vis[],vector<int> adj[])
+{
+    vis[v]=true;
+    for(auto i=adj[v].begin();i!=adj[v].end();i++)
+    {
+        if(vis[*i]==false)
+            calculate_time(*i,st,vis,adj);
+    }
+    st.push(v);
+}
+void dfs(int v,bool vis[],vector<int> grev[])
+{
+    vis[v]=true;
+    // cout<<v<<" ";
+    for(auto i=grev[v].begin();i!=grev[v].end();i++)
+    {
+        if(vis[*i]==false)
+            dfs(*i,vis,grev);
+    }
+}
+int kosaraju(int V, vector<int> adj[])
+{
+    // print(adj,V);
+    bool vis[V]={};
+    stack<int> st;
+    for(int v=0;v<V;v++)
+    {
+        if(vis[v]==false)
+            calculate_time(v,st,vis,adj);
+    }
+    // cout<<"stack_size="<<st.size()<<endl;
+    //making new graph (grev) with reverse edges as in adj[]
+    vector<int> grev[V];
+    for(int i=0;i<V+1;i++)
+    {
+        for(auto j=adj[i].begin();j!=adj[i].end();j++)
+        {
+            grev[*j].push_back(i);
+        }
+    }
+    // cout<<"grev="<<endl;
+    // print(grev,V);
+    //reinitialise visited to 0
+    for(int i=0;i<V;i++)
+        vis[i]=false;
+    int cnt_scc=0;
+    while(!st.empty())
+    {
+        int t=st.top();
+        st.pop();
+        if(vis[t]==false)
+        {
+            dfs(t,vis,grev);
+            cnt_scc++;
+        }
+    }
+    // cout<<"cnt_scc="<<cnt_scc<<endl;
+    return cnt_scc;
+
+}
+//All critical/corner cases have been taken care of.
+//Input your required values: (not hardcoded)
+int main()
+{
+    int t;
+    cin>>t; 
+    while(t--)
+    {
+        int a,b ;
+   	    cin>>a>>b;
+   	    int m,n;
+   	    vector<int> adj[a+1];
+        for(int i=0;i<b;i++)
+        {
+            cin>>m>>n;
+            adj[m].push_back(n);
+        }
+        // exit(0);
+        cout<<kosaraju(a, adj)<<endl;
+    }
+    return 0;
+}

From 0ef5cbec296495d5c4852a5073961f04db6dc4c4 Mon Sep 17 00:00:00 2001
From: Anirban Chetia <bloodraven166@gmail.com>
Date: Thu, 21 Nov 2019 22:11:24 +0530
Subject: [PATCH 2/4] Updated function definitions with comments

function definitions - what it does with its type (iterative/recursive)
common terms/annotations
2 statements marked as debug, removed other comments (as I kept them while coding)
added comments to main function
---
 Graph/Kosaraju.cpp | 54 ++++++++++++++++++++++++++++------------------
 1 file changed, 33 insertions(+), 21 deletions(-)

diff --git a/Graph/Kosaraju.cpp b/Graph/Kosaraju.cpp
index a9131faa8..ca747bdbc 100644
--- a/Graph/Kosaraju.cpp
+++ b/Graph/Kosaraju.cpp
@@ -1,12 +1,20 @@
 /* Implementation of Kosaraju's Algorithm to find out the strongly connected components (SCCs) in a graph. 
    Author:Anirban166
-*/
+*/   
 
 #include<iostream>
 #include<vector>
 
 using namespace std;
 
+/*Common terms/anotations used as parameters in functions below:
+  V: number of vertices,
+  adj[]: array of vectors to represent graph,
+  vis[]: array to keep track of visited nodes, (boolean type)
+  grev[]: graph with reverse edges.
+*/  
+
+//iterative function/method to print graph:
 void print(vector<int> a[],int V)
 {
     for(int i=0;i<V;i++)
@@ -19,16 +27,20 @@ void print(vector<int> a[],int V)
             cout<<endl;
     }
 }
-void calculate_time(int v,stack<int> &st,bool vis[],vector<int> adj[])
+
+//recursive function/method to push vertices into stack passed as parameter: (referenced)
+void push_vertex(int v,stack<int> &st,bool vis[],vector<int> adj[])
 {
     vis[v]=true;
     for(auto i=adj[v].begin();i!=adj[v].end();i++)
     {
         if(vis[*i]==false)
-            calculate_time(*i,st,vis,adj);
+            push_vertex(*i,st,vis,adj);
     }
     st.push(v);
 }
+
+//recursive function/method to implement depth first traversal(dfs):
 void dfs(int v,bool vis[],vector<int> grev[])
 {
     vis[v]=true;
@@ -39,18 +51,18 @@ void dfs(int v,bool vis[],vector<int> grev[])
             dfs(*i,vis,grev);
     }
 }
+
+//function/method to implement Kosaraju's Algorithm:
 int kosaraju(int V, vector<int> adj[])
 {
-    // print(adj,V);
     bool vis[V]={};
     stack<int> st;
     for(int v=0;v<V;v++)
     {
         if(vis[v]==false)
-            calculate_time(v,st,vis,adj);
+            push_vertex(v,st,vis,adj);
     }
-    // cout<<"stack_size="<<st.size()<<endl;
-    //making new graph (grev) with reverse edges as in adj[]
+    //making new graph (grev) with reverse edges as in adj[]:
     vector<int> grev[V];
     for(int i=0;i<V+1;i++)
     {
@@ -59,12 +71,12 @@ int kosaraju(int V, vector<int> adj[])
             grev[*j].push_back(i);
         }
     }
-    // cout<<"grev="<<endl;
-    // print(grev,V);
+    // cout<<"grev="<<endl; ->debug statement
+    // print(grev,V);       ->debug statement
     //reinitialise visited to 0
     for(int i=0;i<V;i++)
         vis[i]=false;
-    int cnt_scc=0;
+    int count_scc=0;
     while(!st.empty())
     {
         int t=st.top();
@@ -72,13 +84,13 @@ int kosaraju(int V, vector<int> adj[])
         if(vis[t]==false)
         {
             dfs(t,vis,grev);
-            cnt_scc++;
+            count_scc++;
         }
     }
-    // cout<<"cnt_scc="<<cnt_scc<<endl;
-    return cnt_scc;
-
+    // cout<<"count_scc="<<count_scc<<endl; //in case you want to print here itself, uncomment & change return type of function to void.
+    return count_scc;
 }
+
 //All critical/corner cases have been taken care of.
 //Input your required values: (not hardcoded)
 int main()
@@ -87,16 +99,16 @@ int main()
     cin>>t; 
     while(t--)
     {
-        int a,b ;
-   	    cin>>a>>b;
-   	    int m,n;
-   	    vector<int> adj[a+1];
-        for(int i=0;i<b;i++)
+        int a,b ; //a->number of nodes, b->directed edges.
+   	  cin>>a>>b;
+   	  int m,n;
+   	  vector<int> adj[a+1];
+        for(int i=0;i<b;i++) //take total b inputs of 2 vertices each required to form an edge.
         {
-            cin>>m>>n;
+            cin>>m>>n; //take input m,n denoting edge from m->n.
             adj[m].push_back(n);
         }
-        // exit(0);
+        //pass number of nodes and adjacency array as parameters to function:
         cout<<kosaraju(a, adj)<<endl;
     }
     return 0;

From 077c758b6e277dcdc634dcb9edf2152ebf5b26a4 Mon Sep 17 00:00:00 2001
From: Anirban Chetia <bloodraven166@gmail.com>
Date: Fri, 22 Nov 2019 22:44:43 +0530
Subject: [PATCH 3/4] Add detailed function definitions (comments)

Updated with proper function definitions
Information about method included
@param parameter : what it is/explanation included
@return return type included
---
 Graph/Kosaraju.cpp | 39 +++++++++++++++++++++++++++++----------
 1 file changed, 29 insertions(+), 10 deletions(-)

diff --git a/Graph/Kosaraju.cpp b/Graph/Kosaraju.cpp
index ca747bdbc..2e66f131f 100644
--- a/Graph/Kosaraju.cpp
+++ b/Graph/Kosaraju.cpp
@@ -7,14 +7,12 @@
 
 using namespace std;
 
-/*Common terms/anotations used as parameters in functions below:
-  V: number of vertices,
-  adj[]: array of vectors to represent graph,
-  vis[]: array to keep track of visited nodes, (boolean type)
-  grev[]: graph with reverse edges.
-*/  
-
-//iterative function/method to print graph:
+/**
+* Iterative function/method to print graph:
+* @param a[] : array of vectors (2D)
+* @param V : vertices
+* @return void 
+**/
 void print(vector<int> a[],int V)
 {
     for(int i=0;i<V;i++)
@@ -28,7 +26,14 @@ void print(vector<int> a[],int V)
     }
 }
 
-//recursive function/method to push vertices into stack passed as parameter: (referenced)
+/**
+* //Recursive function/method to push vertices into stack passed as parameter:
+* @param v : vertices
+* @param &st : stack passed by reference
+* @param vis[] : array to keep track of visited nodes (boolean type)
+* @param adj[] : array of vectors to represent graph
+* @return void 
+**/
 void push_vertex(int v,stack<int> &st,bool vis[],vector<int> adj[])
 {
     vis[v]=true;
@@ -40,7 +45,14 @@ void push_vertex(int v,stack<int> &st,bool vis[],vector<int> adj[])
     st.push(v);
 }
 
-//recursive function/method to implement depth first traversal(dfs):
+
+/**
+* //Recursive function/method to implement depth first traversal(dfs):
+* @param v : vertices
+* @param vis[] : array to keep track of visited nodes (boolean type)
+* @param grev[] : graph with reversed edges
+* @return void 
+**/
 void dfs(int v,bool vis[],vector<int> grev[])
 {
     vis[v]=true;
@@ -53,6 +65,13 @@ void dfs(int v,bool vis[],vector<int> grev[])
 }
 
 //function/method to implement Kosaraju's Algorithm:
+/**
+* Info about the method
+* @param V : vertices in graph
+* @param adj[] : array of vectors that represent a graph (adjacency list/array)
+* @return int ( 0, 1, 2..and so on, only unsigned values as either there can be no SCCs i.e. none(0) or there will be x no. of SCCs (x>0))
+   i.e. it returns the count of (number of) strongly connected components (SCCs) in the graph. (variable 'count_scc' within function)
+**/
 int kosaraju(int V, vector<int> adj[])
 {
     bool vis[V]={};

From ce655b716bbd311ed9d2c5b30f39af3523763979 Mon Sep 17 00:00:00 2001
From: Bhaumik Mistry <Bhaumikpmistry@gmail.com>
Date: Fri, 22 Nov 2019 17:09:52 -0500
Subject: [PATCH 4/4] Rename Kosaraju.cpp to kosaraju.cpp

Change file name.
---
 Graph/{Kosaraju.cpp => kosaraju.cpp} | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
 rename Graph/{Kosaraju.cpp => kosaraju.cpp} (100%)

diff --git a/Graph/Kosaraju.cpp b/Graph/kosaraju.cpp
similarity index 100%
rename from Graph/Kosaraju.cpp
rename to Graph/kosaraju.cpp