shortestpath.java

import java.util.*;

public class MyTest {


    private static int shortestPath(int[] from, int[] to, int source, int destination) {
        Map<Integer, Set<Integer>> graph = getGraph(from, to);
        return iterate(graph, new HashSet<>(), source, destination);
    }

    private static Map<Integer, Set<Integer>> getGraph(int[] from, int[] to) {
        Map<Integer, Set<Integer>> graph = new HashMap<>();

        for (int i = 0; i < from.length; i++) {
            Set<Integer> neighbourhood = graph.getOrDefault(from[i], new HashSet<>());
            neighbourhood.add(to[i]);
            graph.put(from[i], neighbourhood);

        }

        for (int i = 0; i < to.length; i++) {
            Set<Integer> neighbourhood = graph.getOrDefault(to[i], new HashSet<>());
            neighbourhood.add(from[i]);
            graph.put(to[i], neighbourhood);
        }
        return graph;
    }


    private static int iterate(Map<Integer, Set<Integer>> graph, Set<Integer> seenNodes, Integer node, Integer destination) {
        seenNodes.add(node);
        Set<Integer> neighbours = graph.get(node);
        for (Integer neighbour : neighbours) {
            if (!seenNodes.contains(neighbour) && neighbour.equals(destination)) {
                return 1;
            }
        }

        for (Integer neighbour : neighbours) {
            if (!seenNodes.contains(neighbour)) {
                int distance = iterate(graph, seenNodes, neighbour, destination);
                if (distance != -1) {
                    return distance + 1;
                }
            }
        }

        return -1;
    }


    public static void main(String[] args) {
        System.out.println(shortestPath(new int[]{0, 0, 1}, new int[]{1, 2, 3}, 2, 3));
//        System.out.println(shortestPath(new int[]{0, 1}, new int[]{2, 3}, 0, 1));

    }
}