From 3e2c18ed462232c47d3e434e03a4193ec80739d7 Mon Sep 17 00:00:00 2001
From: hkumar0132 <63600554+hkumar0132@users.noreply.github.com>
Date: Mon, 21 Jun 2021 18:18:06 +0530
Subject: [PATCH] chore(CPlusPlus): added breadth first search (#362)

---
 .../CPlusPlus/Graphs/breadth-first-search.cpp | 103 ++++++++++++++++++
 algorithms/CPlusPlus/README.md                |   1 +
 2 files changed, 104 insertions(+)
 create mode 100644 algorithms/CPlusPlus/Graphs/breadth-first-search.cpp

diff --git a/algorithms/CPlusPlus/Graphs/breadth-first-search.cpp b/algorithms/CPlusPlus/Graphs/breadth-first-search.cpp
new file mode 100644
index 00000000..5c1f5bad
--- /dev/null
+++ b/algorithms/CPlusPlus/Graphs/breadth-first-search.cpp
@@ -0,0 +1,103 @@
+// Program to print BFS traversal from a given
+// source vertex. BFS(int s) traverses vertices
+// reachable from s.
+#include<iostream>
+#include <list>
+ 
+using namespace std;
+ 
+// This class represents a directed graph using
+// adjacency list representation
+class Graph
+{
+    int V;    // No. of vertices
+ 
+    // Pointer to an array containing adjacency
+    // lists
+    list<int> *adj;  
+public:
+    Graph(int V);  // Constructor
+ 
+    // function to add an edge to graph
+    void addEdge(int v, int w);
+ 
+    // prints BFS traversal from a given source s
+    void BFS(int s); 
+};
+ 
+Graph::Graph(int V)
+{
+    this->V = V;
+    adj = new list<int>[V];
+}
+ 
+void Graph::addEdge(int v, int w)
+{
+    adj[v].push_back(w); // Add w to v’s list.
+}
+ 
+void Graph::BFS(int s)
+{
+    // Mark all the vertices as not visited
+    bool *visited = new bool[V];
+    for(int i = 0; i < V; i++)
+        visited[i] = false;
+ 
+    // Create a queue for BFS
+    list<int> queue;
+ 
+    // Mark the current node as visited and enqueue it
+    visited[s] = true;
+    queue.push_back(s);
+ 
+    // 'i' will be used to get all adjacent
+    // vertices of a vertex
+    list<int>::iterator i;
+ 
+    while(!queue.empty())
+    {
+        // Dequeue a vertex from queue and print it
+        s = queue.front();
+        cout << s << " ";
+        queue.pop_front();
+ 
+        // Get all adjacent vertices of the dequeued
+        // vertex s. If a adjacent has not been visited,
+        // then mark it visited and enqueue it
+        for (i = adj[s].begin(); i != adj[s].end(); ++i)
+        {
+            if (!visited[*i])
+            {
+                visited[*i] = true;
+                queue.push_back(*i);
+            }
+        }
+    }
+}
+ 
+// Driver program to test methods of graph class
+int main()
+{
+    // Create a graph given in the above diagram
+
+    int edges;
+    cout << "Enter number of edges: ";
+    cin >> edges;
+    Graph g(edges);
+
+    for(int i = 0; i < edges; i++) {
+        int u, v;
+        cout << "Enter an edge: ";
+        cin >> u >> v;
+        g.addEdge(u, v);
+    }
+
+    cout << "Following is Breadth First Traversal "
+         << "(starting from vertex 0) \n";
+    g.BFS(0);
+ 
+    return 0;
+}
+
+//Time complexity: O(n), where n is the number of vertices in graph
+//Space complexity: O(n), where n is the number of vertices in graph
\ No newline at end of file
diff --git a/algorithms/CPlusPlus/README.md b/algorithms/CPlusPlus/README.md
index 17fd91f8..64d91640 100644
--- a/algorithms/CPlusPlus/README.md
+++ b/algorithms/CPlusPlus/README.md
@@ -14,6 +14,7 @@
 ## Graphs
 1. [Bellman Ford Algorithm](Graphs/bellmam-ford.cpp)
 2. [kruskal Algorithm](Graphs/kruskal-algorithm.cpp)
+3. [Breadth First Search](Graphs/breadth-first-search.cpp)
 
 ## Multiplication
 1. [Karatsuba](Multiplication/karatsuba.cpp)