Merge pull request #240 from tpriyanshu90/master

BFS in java

Author: probot-auto-merge[bot]

Graph Traversal/BFS/BFS.java

@@ -0,0 +1,101 @@
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+public class BFS{
+  public static void main(String[] args){
+    Graph G = new Graph();
+    G.addEdge(1,2);
+    G.addEdge(1,3);
+    G.addEdge(1,4);
+    G.addEdge(4,5);
+    G.addEdge(4,6);
+    G.addEdge(2,7);
+
+    List<Node> BFSresult = G.breadthFirstSearch(1); //1 is the root from where we start BFS
+
+    //printing the result
+    for(Node nodes : BFSresult){
+      System.out.println(nodes.getName());
+    }
+  }
+}
+
+class Graph {
+  private Map<Integer, Node> nodes = new HashMap<Integer, Node>();
+
+  public Graph() {}
+
+  public void addEdge(Integer nodeName1, Integer nodeName2) {
+    Node node1 = nodes.get(nodeName1);
+    if (node1 == null) {
+      node1 = new Node(nodeName1);
+    }
+
+    Node node2 = nodes.get(nodeName2);
+    if (node2 == null) {
+      node2 = new Node(nodeName2);
+    }
+
+    node1.addNeighbor(node2);
+    node2.addNeighbor(node1);
+
+    nodes.put(nodeName1, node1);
+    nodes.put(nodeName2, node2);
+  }
+
+  public List<Node> breadthFirstSearch(int rootName) {
+    List<Node> result = new ArrayList<Node>();
+    List<Node> temp = new ArrayList<Node>();
+    Set<Integer> visited = new HashSet<Integer>();
+
+    Node root = nodes.get(rootName);
+    temp.add(root);
+    visited.add(rootName);
+
+    while (temp.size() > 0) {
+      Node currentNode = temp.get(0);
+      List<Node> neighbors = currentNode.getNeighbors();
+
+      for (int i = 0; i < neighbors.size(); i++) {
+        Node neighbor = neighbors.get(i);
+        // a node can only be visited once if it has more than one parents
+        if (visited.contains(neighbor.getName())) {
+          continue;
+        } else {
+          temp.add(neighbor);
+          visited.add(neighbor.getName());
+        }
+      }
+
+      temp.remove(0);
+      result.add(currentNode);
+    }
+
+    return result;
+  }
+}
+
+class Node {
+  Integer name;
+  List<Node> neighbors = new ArrayList<Node>();
+
+  public Node(Integer name) {
+    this.name = name;
+  }
+
+  public Integer getName() {
+    return this.name;
+  }
+
+  public void addNeighbor(Node neighbor) {
+    neighbors.add(neighbor);
+  }
+
+  public List<Node> getNeighbors() {
+    return neighbors;
+  }
+}