## BFS Distance

Explanation

This is an answer for a HackerRank question - Breadth First Search: Shortest Reach.

Consider an undirected graph where each edge is the same weight. Each of the nodes is labeled consecutively.

You will be given a number of queries. For each query, you will be given a list of edges describing an undirected graph. After you create a representation of the graph, you must determine and report the shortest distance to each of the other nodes from a given starting position using the breadth-first search algorithm (BFS). Distances are to be reported in node number order, ascending. If a node is unreachable, print -1 for that node. Each of the edges weighs 6 units of distance.

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import java.util.*;
public class BFSGraph {
class Node {
int value;
int distance;
Node(int v, int d) {
value = v;
distance = d;
}
}
LinkedList<Integer>[] m_graph;
int m_size;
BFSGraph(int size) {
m_size = size;
m_graph = new LinkedList[size];
for (int i = 0; i < m_size; i++) {
m_graph[i] = new LinkedList<Integer>();
}
}
void addEdge(int i, int j) {
m_graph[i].add(j);
m_graph[j].add(i);
}
int distance(int start, int end) {
if (start == end) {
return 0;
}
Queue<Node> myQueue = new LinkedList<Node>();
myQueue.add(new Node(start, 0));
Map<Integer, Boolean> visited = new HashMap<Integer, Boolean>();
while (myQueue.size() > 0) {
Node current = myQueue.poll();
//current.distance++;
for (int i = 0; i < m_graph[current.value].size(); i++) {
int child = m_graph[current.value].get(i);
if (child == end) {
current.distance++;
return current.distance;
}
if (! visited.containsKey(child)) {
visited.put(child, true);
myQueue.add(new Node(child, current.distance+1));
}
}
}
return -1;
}
public static void main (String args[]) {
Scanner stdin = new Scanner(System.in);
//int queries = stdin.next();
String[] arr = stdin.nextLine().trim().split("\\s+");
int queries = Integer.parseInt(arr[0]);
for (int i = 0; i < queries; i++) {
arr = stdin.nextLine().trim().split("\\s+");
int size = Integer.parseInt(arr[0]);
int edges = Integer.parseInt(arr[1]);
BFSGraph bfsGraph = new BFSGraph(size + 1);
for (int j = 0; j < edges; j++) {
arr = stdin.nextLine().trim().split("\\s+");
int x = Integer.parseInt(arr[0]);
int y = Integer.parseInt(arr[1]);
bfsGraph.addEdge(x, y);
}
arr = stdin.nextLine().trim().split("\\s+");
int startNode = Integer.parseInt(arr[0]);
for (int x = 1; x < size + 1; x++) {
if (x != startNode) {
int value = bfsGraph.distance(startNode, x);
if (value != -1) {
System.out.printf("%d ", 6*value);
}
else {
System.out.printf("%d ", value);
}
}
}
System.out.println();
}
}
}