From f2f6b3c1f3fe5c32d65ef2f30526c9843c14be5c Mon Sep 17 00:00:00 2001
From: Abhishek Upadhayay <52717415+mr-abhi-k@users.noreply.github.com>
Date: Fri, 23 Oct 2020 09:38:12 +0530
Subject: [PATCH 1/2] added most suitable bfs for competitive programing

---
 .../cpp/bfs for competitive programming.cpp   | 134 ++++++++++++++++++
 1 file changed, 134 insertions(+)
 create mode 100644 Graphs/bfs/cpp/bfs for competitive programming.cpp

diff --git a/Graphs/bfs/cpp/bfs for competitive programming.cpp b/Graphs/bfs/cpp/bfs for competitive programming.cpp
new file mode 100644
index 000000000..24a62f100
--- /dev/null
+++ b/Graphs/bfs/cpp/bfs for competitive programming.cpp	
@@ -0,0 +1,134 @@
+#include<bits/stdc++.h>  //includes all libraries mainly used in CP
+using namespace std;
+
+/*
+CODE INTRO:--
+this code has 3 functions:
+1st- for adding edge
+2nd- for printing graph as adjacency list
+3rd- bfs implementation
+*/
+
+/*
+
+addedge function:
+Arguments : 1.adjacency list(adj), 2.first vertex(u), 3.second vertex(v), 4.bool value(twoWay) to check whether itis directed or undirected
+then fills list as u-->v
+if undirected twoWay will be true and,
+v-->u will also gets implemented
+
+*/
+
+void addedge(vector<vector<int>>  &adj, int u, int v, bool twoWay)
+{
+     adj[u].push_back(v);//u-->v
+     if(twoWay)
+     adj[v].push_back(u);//v-->u
+} 
+
+/*
+
+printgraph function:
+Arguments : 1.adjacency list, 2.no. of vertex(n)
+loops through whole vertex and goes inside the list of particular vertex to print all vertices
+e.g:
+[1]-->3-->4-->5
+ |
+[2]-->1-->3-->6
+ |
+[3]-->4-->3
+
+o/p will be : 1->3->4->5->2->6
+
+*/
+
+void printgraph( vector<vector<int>> &adj, int n)
+{
+    for(int v=0;v<n;++v)//for looping no. of vertex basically nodes of array list
+    {
+        cout<<"all vertex of list - "<<v<<" are: "<<endl;
+        cout<<"head->";
+        for(auto x:adj[v])//loops through particular vertex
+        cout<<"->"<<x;
+        cout<<endl;
+    }
+}
+
+/*
+
+bfs function:
+Arguments : 1.adjacency list(adj), 2.no. of vertices(n), 3.source vertex(s) from where u want ur bfs to start
+it uses,
+queue q: for taking all vertex one-by-one
+bool vector used: for marking visited nodes
+int vector d: for storing the distance of particular vertex from start
+int vector p: for storing the parnet of particular vector 
+int vector path: to get the shortest path
+
+*/
+void bfs(const vector<vector<int>> &adj,int n, int s)
+{
+    //vector<vector<int>> adj  adjacency list representation
+    //int n  no. of nodes
+    //int s  source vetex
+    queue<int> q;
+    vector<bool> used(n); //for marking visited nodes
+    vector<int> d(n), p(n); //for distance and parent
+    vector<int>path;
+    q.push(s);//first pushes this source vertex to the queue to find all the connected vertices of s
+    used[s]=true;//marked visited
+    p[s]=-1;
+    d[s]=0;
+    while(!q.empty())//loop until queue becomes empty
+    {
+        int v=q.front();//take first vertex of queue
+        path.push_back(v);//push it into path vector
+        q.pop();
+        for(int u : adj[v])//find all vertices connected with that vertex
+        {
+            //for traversing
+            if(!used[u])//if that vertex is not visited make it visit
+            {
+                used[u]=true;
+                q.push(u);
+                d[u]=d[v]+1;//find distance
+                p[u]=v;//find parent
+            }
+        }
+    }
+    cout<<"path :";//prints shortest path
+    for(auto x:path)
+    cout<<x<<" ";
+}
+
+int main()
+{
+   
+
+    int n1,n2;
+    cout<<"enter no. of nodes : ";
+    cin>>n1;
+    cout<<"enter no. of edges :";
+    cin>>n2;
+    cout<<"enter vertex";
+    int u,v;
+    vector<vector<int>> adj(n1+1);//adjacency list 
+    char ch;
+    for(int i=0;i<n2;i++)
+    {
+        cout<<"enter two vertex :\n";
+        cin>>u;
+        cin>>v;
+        cout<<"y: undirected -";
+        cin>>ch;
+        if(ch=='y')
+        addedge(adj,u,v,true);
+        else
+        addedge(adj,u,v,false);
+    }
+     printgraph(adj,n1);
+     cout<<"enter the sorce vertex : ";
+     int s;
+     cin>>s;
+     bfs(adj,n1,s);//finds bfs
+}
\ No newline at end of file

From ec60363525389702a53da86b16700b34bb0b83c4 Mon Sep 17 00:00:00 2001
From: Abhishek Upadhayay <52717415+mr-abhi-k@users.noreply.github.com>
Date: Fri, 23 Oct 2020 09:39:35 +0530
Subject: [PATCH 2/2] Update bfs for competitive programming.cpp

---
 Graphs/bfs/cpp/bfs for competitive programming.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Graphs/bfs/cpp/bfs for competitive programming.cpp b/Graphs/bfs/cpp/bfs for competitive programming.cpp
index 24a62f100..d9e3276bf 100644
--- a/Graphs/bfs/cpp/bfs for competitive programming.cpp	
+++ b/Graphs/bfs/cpp/bfs for competitive programming.cpp	
@@ -119,7 +119,7 @@ int main()
         cout<<"enter two vertex :\n";
         cin>>u;
         cin>>v;
-        cout<<"y: undirected -";
+        cout<<"y: undirected -";// asks for directed or undirected
         cin>>ch;
         if(ch=='y')
         addedge(adj,u,v,true);
@@ -131,4 +131,4 @@ int main()
      int s;
      cin>>s;
      bfs(adj,n1,s);//finds bfs
-}
\ No newline at end of file
+}