src/main/BFS.java


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import java.util.ArrayList;
import java.util.Arrays;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;

public class BFS {
    private static int distance(ArrayList<Integer>[] adj, int s, int t) {
        int[] dist = new int[adj.length];
        Arrays.fill(dist, -1);
        dist[s] = 0;

        bfs(adj, s, dist);

        return dist[t];
    }

    private static void bfs(ArrayList<Integer>[] adj, int s, int[] dist) {
        Queue<Integer> vertexQ = new LinkedList<>();
        vertexQ.add(s);

        while (!vertexQ.isEmpty()) {
            int u = vertexQ.remove();
            for (int i : adj[u]) {
                if (dist[i] == -1) {
                    vertexQ.add(i);
                    dist[i] = dist[u] + 1;
                }
            }
        }
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int m = scanner.nextInt();
        ArrayList<Integer>[] adj = (ArrayList<Integer>[]) new ArrayList[n];
        for (int i = 0; i < n; i++) {
            adj[i] = new ArrayList<Integer>();
        }
        for (int i = 0; i < m; i++) {
            int x, y;
            x = scanner.nextInt();
            y = scanner.nextInt();
            adj[x - 1].add(y - 1);
            adj[y - 1].add(x - 1);
        }
        int x = scanner.nextInt() - 1;
        int y = scanner.nextInt() - 1;
        System.out.println(distance(adj, x, y));
    }
}