src/main/ConnectedComponents.java


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import java.util.ArrayList;
import java.util.Scanner;

public class ConnectedComponents {

    static int numberOfComponents(ArrayList<ArrayList<Integer>> adj) {
        ArrayList<Integer> visited = new ArrayList<>();
        int cc = 0;
        for (int v = 0; v < adj.size(); v++) {
            if (!visited.contains(v)) {
                explore(adj, visited, v);
                cc++;
            }
        }
        return cc;
    }

    private static void explore(ArrayList<ArrayList<Integer>> adj, ArrayList<Integer> visited, int v) {
        visited.add(v);

        for (int n : adj.get(v)) {
            if (!visited.contains(n))
                explore(adj, visited, n);
        }
    }

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