Algorithms 1 Social network connectivity

TestRunner.java

import java.util.EmptyStackException;
import java.util.HashMap;

class MemberLogItem {
    public int timestamp = 0;
    public int follower = 0;
    public int followee = 0;

    public MemberLogItem(int timestamp, int follower, int followee) {
        this.timestamp = timestamp;
        this.follower = follower;
        this.followee = followee;
    }
}

public class Percolation {

    private int members[] = new int[]{ 1,2,3,4,5,6,7,8,9,10 };
    private int numberOfRoots = members.length;
    private MemberLogItem[] memberLogItems;
    private HashMap<Integer, Integer> memberRelations = new HashMap<Integer, Integer>();

    public void setMemberLogItems(MemberLogItem[] memberLogItems) {
        this.memberLogItems = memberLogItems;
    }

    private int findRoot(int memberId) {
        boolean foundRoot = false;
        int rootId = memberId;
        while(!foundRoot) {
            int newId = memberRelations.get(rootId);
            if(newId == memberRelations.get(newId)) {
                foundRoot = true;
            } 
            rootId = newId;
        }
        return rootId;
    }

    private void makeFriends(int follower, int followee) {
        int followerRoot = findRoot(follower);
        int followeeRoot = findRoot(followee);
        if(followerRoot != followeeRoot) {
            numberOfRoots--;
            memberRelations.put(followerRoot, followeeRoot);
        }
    }

    public int solve() {
        for(int i = 0; i < memberLogItems.length; i++) {
            MemberLogItem memberLogItem = memberLogItems[i];
            Integer followerRelation = memberRelations.get(memberLogItem.follower);
            if(followerRelation == null) {
                memberRelations.put(memberLogItem.follower, memberLogItem.follower);
            }
            Integer followeeRelation = memberRelations.get(memberLogItem.followee);
            if(followeeRelation == null) {
                memberRelations.put(memberLogItem.followee, memberLogItem.followee);
            }
            makeFriends(memberLogItem.follower, memberLogItem.followee);
            if(numberOfRoots == 1) {
                return memberLogItem.timestamp;
            }
        }
        // If this error gets thrown, no solutions were found.
        throw new EmptyStackException();
    }
}

public class TestRunner {
    public static void main(String[] args) {
        Percolation percolation = new Percolation();
        final MemberLogItem[] memberLogItems = new MemberLogItem[12];
        memberLogItems[0] = new MemberLogItem(1234, 1, 5);
        memberLogItems[1] = new MemberLogItem(1235, 2, 3);
        memberLogItems[2] = new MemberLogItem(1236, 1, 6);
        memberLogItems[3] = new MemberLogItem(1237, 5, 7);
        memberLogItems[4] = new MemberLogItem(1238, 9, 4);
        memberLogItems[5] = new MemberLogItem(1239, 8, 2);
        memberLogItems[6] = new MemberLogItem(1240, 10, 1);
        memberLogItems[7] = new MemberLogItem(1241, 5, 3);
        memberLogItems[8] = new MemberLogItem(1242, 3, 8);
        memberLogItems[9] = new MemberLogItem(1243, 9, 1);
        memberLogItems[10] = new MemberLogItem(1244, 9, 2);
        memberLogItems[11] = new MemberLogItem(1245, 9, 3);
        percolation.setMemberLogItems(memberLogItems);
        System.out.println(percolation.solve());
    }
}