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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.*;
  4. import java.lang.*;
  5. import java.io.*;
  6. import java.security.MessageDigest;
  7. import java.nio.charset.StandardCharsets;
  8.  
  9.  
  10. /* Name of the class has to be "Main" only if the class is public. */
  11. class Ideone
  12. {
  13.  
  14. public static class Ring {
  15.  
  16.     public static class OrderedMemberRing {
  17.  
  18.         public static OrderedMemberRing ofOnlineMembers(HashSet<String> onlineMembers, String ownName, String hashModification) {
  19.             HashMap<Integer, String> hashToMember = new HashMap<>();
  20.             for(String member : onlineMembers) {
  21.                 int hash = hashOf(member, hashModification);
  22.                 if(hashToMember.containsKey(hash)) {
  23.                     // Hash collision, can't determine next
  24.                     return null;
  25.                 }
  26.                 hashToMember.put(hash, member);
  27.             }
  28.             if(ownName != null) {
  29.                 int ownHash = hashOf(ownName, hashModification);
  30.                 if(!hashToMember.containsKey(ownHash))
  31.                     hashToMember.put(ownHash, ownName);
  32.             }
  33.             ArrayList<Integer> orderedHashes = new ArrayList<>(hashToMember.keySet());
  34.             Collections.sort(orderedHashes);
  35.  
  36.             ArrayList<String> orderedMembers = new ArrayList<>();
  37.             for(int hash : orderedHashes)
  38.                 orderedMembers.add(hashToMember.get(hash));
  39.             return new OrderedMemberRing(orderedMembers.toArray(new String[0]), hashModification);
  40.         }
  41.  
  42.         private final String[] ring;
  43.         private final String usedHashModification;
  44.  
  45.         public OrderedMemberRing(String[] ring, String usedHashModification) {
  46.             this.ring = ring;
  47.             this.usedHashModification = usedHashModification;
  48.         }
  49.  
  50.         public String[] getRing() {
  51.             return ring;
  52.         }
  53.  
  54.         public String getUsedHashModification() {
  55.             return usedHashModification;
  56.         }
  57.  
  58.         /**
  59.          * @return -1 if not found. Else index of member in orderedMemberRing
  60.          */
  61.         public int indexOf(String member) {
  62.             int memberIndex = -1;
  63.             for(int i = 0; i < ring.length; i++) {
  64.                 if(ring[i].equalsIgnoreCase(member)) {
  65.                     memberIndex = i;
  66.                     break;
  67.                 }
  68.             }
  69.             return memberIndex;
  70.         }
  71.  
  72.         public boolean contains(String member) {
  73.             return indexOf(member) != -1;
  74.         }
  75.  
  76.         public String after(String member) {
  77.             int memberIndex = indexOf(member);
  78.             if(memberIndex == -1) return null; // Not found!
  79.             return ring[Math.floorMod(memberIndex + 1, ring.length)];
  80.         }
  81.  
  82.         public String before(String member) {
  83.             int memberIndex = indexOf(member);
  84.             if(memberIndex == -1) return null; // Not found!
  85.             return ring[Math.floorMod(memberIndex - 1, ring.length)];
  86.         }
  87.     }
  88.  
  89.     public static int hashOf(String userName, String hashModification) {
  90.         userName = userName.toLowerCase();
  91.         String hashStr = userName + (hashModification != null ? ":" + hashModification : "");
  92.         // Create MD5 Hash
  93.         try {
  94.             MessageDigest digest = java.security.MessageDigest.getInstance("MD5");
  95.             byte[] hash = digest.digest(hashStr.getBytes(StandardCharsets.UTF_8));
  96.             int h = (hash[0] << 3*8) | (hash[1] << 2*8) | (hash[2] << 8) | (hash[3]);
  97.             System.out.println(userName + " : " + h + " : " + hash[3]);
  98.             return h;
  99.         }catch (Exception ex) {
  100.             throw new RuntimeException("WTF, this should never happen! You don't have MD5!");
  101.         }
  102.     }
  103.  
  104.     public static boolean contains(HashSet<String> members, String member) {
  105.         for(String maybeMember : members)
  106.             if(maybeMember.equalsIgnoreCase(member)) return true;
  107.         return false;
  108.     }
  109.  
  110. }
  111.  
  112.  
  113. 	public static void main (String[] args) throws java.lang.Exception
  114. 	{
  115. 		HashSet<String> members = new HashSet<>();
  116. 		members.add("EnderKill98");
  117. 		members.add("ItzN00bPvP");
  118. 		members.add("GoobBot1");
  119. 		members.add("Honbra");
  120. 		var r = Ring.OrderedMemberRing.ofOnlineMembers(members, "EnderKill98", "rwgOSa");
  121. 		for(String member : r.getRing()) {
  122. 			System.out.println(" - "  + member);
  123. 		}
  124. 	}
  125. }
  126.  
Success #stdin #stdout 0.22s 61388KB
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stdin
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stdout
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goobbot1 : -34 : -34
enderkill98 : -78 : -78
itzn00bpvp : -118 : -118
honbra : -105 : -105
enderkill98 : -78 : -78
 - ItzN00bPvP
 - Honbra
 - EnderKill98
 - GoobBot1
https://ideone.com/Uyqh2c
language:
Java (HotSpot 12)
created:
189 days ago
visibility:
secret

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