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Graph_BFSTraversalOfGraph.java
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Graph_BFSTraversalOfGraph.java
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import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
// 09.07.2020
// https://practice.geeksforgeeks.org/problems/bfs-traversal-of-graph/1
// https://www.geeksforgeeks.org/breadth-first-search-or-bfs-for-a-graph/
// https://www.youtube.com/watch?v=60yo4vvRU5s
class Graph_BFSTraversalOfGraph {
private static List<Integer> bfs(List<List<Integer>> adjList, int noOfVertexes) {
boolean[] isVisited = new boolean[noOfVertexes];
LinkedList<Integer> queue = new LinkedList<>();
List<Integer> listOfNodes = new ArrayList<>();
int startingNode = 0;
isVisited[startingNode] = true;
queue.add(startingNode);
while(!queue.isEmpty()) {
startingNode = queue.poll();
listOfNodes.add(startingNode);
for (int node : adjList.get(startingNode)) {
if (!isVisited[node]) {
isVisited[node] = true;
queue.add(node);
}
}
}
return listOfNodes;
}
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int t = Integer.parseInt(br.readLine().trim());
while(t-->0) {
String[] nm = br.readLine().trim().split("\\s+");
int noOfVertexes = Integer.parseInt(nm[0]);
int noOfEdges = Integer.parseInt(nm[1]);
String[] edges = br.readLine().trim().split("\\s+");
List<List<Integer>> adjList = getAdjacencyList(noOfVertexes, edges);
List<Integer> result = bfs(adjList, noOfVertexes);
print(result);
}
}
private static List<List<Integer>> getAdjacencyList(int noOfVertexes, String[] edges) {
List<List<Integer>> adjList = new ArrayList<>();
for (int i = 0; i < noOfVertexes; i++) {
adjList.add(i, new ArrayList<>());
}
for (int i = 0; i < edges.length; i+=2) {
int sourceNode = Integer.parseInt(edges[i]);
int destinationNode = Integer.parseInt(edges[i+1]);
adjList.get(sourceNode).add(destinationNode); // it is a directed graph
}
return adjList;
}
private static void print(List<Integer> result) {
StringBuilder sb = new StringBuilder();
for (int node : result) {
sb.append(node + " ");
}
System.out.println();
}
}
// below is the OLD IMPLEMENTATION
/*
class BFS_ofGraph {
static class Graph {
int v;
LinkedList<Integer> adjListArray[];
Graph(int v){
this.v = v;
adjListArray = new LinkedList[v];
for (int i = 0; i < v; i++) {
adjListArray[i] = new LinkedList<>();
}
}
}
static void addEdges(Graph graph, int src, int dest) {
graph.adjListArray[src].add(dest);
graph.adjListArray[dest].add(src);
}
static void bfs(Graph graph,int s) {
boolean visited[] = new boolean[graph.v];
LinkedList<Integer> queue = new LinkedList<>();
visited[s] = true;
queue.add(s);
while(!queue.isEmpty()) {
s = queue.poll();
System.out.print(s+" ");
Iterator<Integer> i = graph.adjListArray[s].listIterator();
while(i.hasNext()) {
int n = i.next();
if(!visited[n]) {
visited[n] = true;
queue.add(n);
}
}
}
System.out.println();
}
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int t = Integer.parseInt(br.readLine().trim());
while(t-->0) {
int n = Integer.parseInt(br.readLine().trim());
String ip[] = br.readLine().trim().split("\\s+");
Graph graph = new Graph(2*n);
for (int i = 0; i < 2*n; i+=2) {
//System.out.println(i);
int src = Integer.parseInt(ip[i]);
int dest = Integer.parseInt(ip[i+1]);
addEdges(graph, src, dest);
}
bfs(graph,Integer.parseInt(ip[0]));
}
}
}
*/