added bfs code

C++14/Graphs/Basics/BFS.cpp

@@ -0,0 +1,52 @@
+#include<bits/stdc++.h>
+using namespace std;
+#define int long long int
+#define endl '\n'
+#define mod 1000000007
+
+void bfs(vector<int> *g, int start,int  *vis)
+{
+	queue<int> q;
+	q.push(start);				// print starting node
+	cout<<start<<" ";			// print starting node
+	vis[start]++;				// Mark vis[start] as visited
+	while(!q.empty())
+	{
+		int front=q.front();	// storing front element
+		q.pop();				// poping the front element
+		for(int i=0;i<g[front].size();i++)		// Traversing all directly connected nodes to node front
+		{
+			if(!vis[g[front][i]])				// Checking if the node is not been already visited
+			{
+				vis[g[front][i]]++;				// Making the node visited
+				cout<<g[front][i]<<" ";			// printing the node
+				q.push(g[front][i]);			// pushing the node to queue
+			}
+		}
+	}
+}
+int32_t main()
+{
+    ios_base::sync_with_stdio(false);
+    cin.tie(NULL);
+    cout.tie(NULL);
+    #ifndef ONLINE_JUDGE
+    // for getting input from input.txt
+    freopen("input.txt", "r", stdin);
+    // for writing output to output.txt
+    freopen("output.txt", "w", stdout);
+    #endif
+
+    int n,m,x,y;
+    cin>>n>>m;   				// n -> Number of Nodes ,, m -> Number of edges
+    vector<int> g[n+1];			// An array of type vector of size N such that g[i] signifies the nodes connected to node i
+    int vis[n+1]={};			// An array to check which nodes are visited and which are remained
+    for(int i=0;i<m;i++)
+    {
+    	cin>>x>>y;         		// defines that there is a bidirectional edge between Node x and Node y
+    	g[x].push_back(y);		// pushing y in g[x] which signifies that there is and edge from x to y
+    	g[y].push_back(x);		// pushing x in g[y] which signifies that there is and edge from y to x
+    }
+    bfs(g,1,vis);					// Calling BFS from starting Node 1
+	return 0;
+}

C++14/Maths/Basics/sieve-of-eratosthenes.cpp

@@ -0,0 +1,44 @@
+#include<bits/stdc++.h>
+using namespace std;
+#define int long long int
+#define endl '\n'
+#define mod 1000000007
+
+bool prime[1000001];
+void sieve(int n)
+{
+	for(int i=2;i<=n;i++)
+		prime[i]=true;					// setting all values as true
+	for(int i=2;i<=sqrt(n);i++)
+	{
+		if(prime[i])
+		{
+			// Update all multiples of i greater than or equal to the square of it 
+            		// numbers which are multiple of i and are less than i^2 are already been marked.  
+			for(int j=i*i;j<=n;j+=i)
+				prime[j]=false;
+		}
+	}
+}
+int32_t main()
+{
+    ios_base::sync_with_stdio(false);
+    cin.tie(NULL);
+    cout.tie(NULL);
+    #ifndef ONLINE_JUDGE
+    // for getting input from input.txt
+    freopen("input.txt", "r", stdin);
+    // for writing output to output.txt
+    freopen("output.txt", "w", stdout);
+    #endif
+
+    int n;
+    cin>>n;
+    sieve(n);
+    for(int i=1;i<=n;i++)
+    {
+    	if(prime[i])
+    		cout<<i<<" ";			// printing the prime numbers till n
+    }
+	return 0;
+}