Question

I have a class Group. In the class I have two fields, idGroup IdGroupGroup. Groups may be part of other groups. My class Group is defined in a HashMap<Integer,Integer>; the key is IdGroupGroup and value is idGroup. I want to search the map for a particular idGroup; can I use recursion to do this?

class Group
{

    int idGroupe
    String word
}

HashMap<Integer,Integer> GroupeGroupe = new HashMap<Integer,Integer>();
GroupeGroupe.put(idGroupeGroupe, idGroupe)

Answer 1

Given a vague question, I have to guess a lot, but perhaps it’s something like this you’re looking for:

import java.util.*;

public class Test {

    static Map<Integer, Integer> groups = new HashMap<Integer, Integer>();

    public static void main(String... args) {
        groups.put(1, 2);
        groups.put(2, 3);
        groups.put(2, 4);
        groups.put(4, 5);
        System.out.println(searchFor(1, 5));
    }

    private static String searchFor(int from, int target) {

        // Target found?
        if (from == target) return "" + target;

        // Dead end?
        if (!groups.containsKey(from)) return null;

        // Recurse and try to find it from here.
        String path = searchFor(groups.get(from), target);
        return path == null ? null : from + " -> " + path;
    }
}

Output:
1 -> 2 -> 4 -> 5

---

Or something like this:

    static Map<Integer, Group> groups = new HashMap<Integer, Group>();

    public static void main(String... args) {
        groups.put(0, new Group(1, "hello")); // (0: -)       -> (1: "hello")
        groups.put(2, new Group(9, "!"));     // (2: "world") -> (9, "!")
        groups.put(3, new Group(5, "bye"));   // (3: -)       -> (5, "bye")
        groups.put(1, new Group(2, "world")); // (1: "hello") -> (2: "world")
        System.out.println(traverse(0));
    }

    private static String traverse(int from) {
        if (!groups.containsKey(from)) return "";

        String path = traverse(groups.get(from).idGroupe);
        return path == null ? null : groups.get(from).word + " " + path;
    }
}

Which prints:

hello world !