Merge pull request #21 from hg398/master

Added BFS in Graphs [C++] Referring issue#15

Author: piyush6348

Graphs/BFS.cpp

@@ -0,0 +1,49 @@
+//written by hg398
+
+#include <bits/stdc++.h>
+using namespace std;
+vector <int> adj[100000];                                            //vector to implement graph using adjacency lists (size can vary a/c to need)
+bool mark[100000];                                                   //array to keep record of visited nodes
+void bfs(int s)
+{
+    queue <int> q;                                                   // Create a queue for BFS
+    mark[s] = true;                                                  // Mark the current node as visited and enqueue it
+    q.push(s);
+                                                
+    while(!q.empty())
+    {
+        s = q.front();                                               // Dequeue a vertex from queue and print it
+        cout << s+1 << " ";
+        q.pop();
+ 
+        // Get all adjacent vertices of the dequeued vertex s
+        // If a adjacent has not been visited, then mark it visited
+        // and enqueue it
+        for(int i = 0; i < adj[s].size(); ++i)
+        {
+            if(!mark[adj[s][i]])
+            {
+                mark[adj[s][i]] = true;
+                q.push(adj[s][i]);
+            }
+        }
+    }
+}
+
+int main() {
+	int nodes,edges;                                                 //no. of nodes and edges in graph
+	cin>>nodes>>edges;
+	while(edges--)
+	{
+		int a,b;                                                     //vertices between which an edge exist
+		cin>>a>>b;
+		a--;b--;                                                     //0-based indexing
+		adj[a].push_back(b);                                         //adding b to adjacency list of a to which it is directly connected 
+		adj[b].push_back(a);                                         //adding a to adjacency list of b to which it is directly connected
+	}
+	memset(mark,false,sizeof(mark));                                 //marking all vertices unvisited
+	int source;                                                      //source node
+	cin>>source;
+	bfs(source);                                                           
+	return 0;
+}