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  1. import java.util.*;
  2. import java.util.concurrent.ThreadLocalRandom;
  3. import java.util.function.Consumer;
  4. import java.util.stream.IntStream;
  5.  
  6. class Ideone
  7. {
  8.   public static void main (String[] args) throws java.lang.Exception
  9.   {
  10.     System.out.println("shuffle, all permutations seen after: " + permutations(Collections::shuffle) + " avg");
  11.     System.out.println("sort, all permutations seen after: " + permutations(list -> list.sort(randomOrder())) + " avg");
  12.   }
  13.  
  14.   private static double permutations(Consumer<List<String>> shuffle) {
  15.     final int expectedPermutations = 6;
  16.     return IntStream.generate(() -> {
  17.       int steps;
  18.       HashSet<List<?>> seen = new HashSet<>();
  19.       for(steps = 0; seen.size() < expectedPermutations; steps++) {
  20.         List<String> l = Arrays.asList("a", "b", "c");
  21.         shuffle.accept(l);
  22.         seen.add(l);
  23.       }
  24.       return steps;
  25.     }).limit(1000).average().orElse(0);
  26.   }
  27.  
  28.   public static Comparator<String> randomOrder() {
  29.       ThreadLocalRandom r = ThreadLocalRandom.current();
  30.       int x = r.nextInt(), y = r.nextInt(), z = r.nextInt();
  31.       boolean b = r.nextBoolean();
  32.       return Comparator.comparingInt((String s) -> Integer.reverse((s.hashCode()&x)^y))
  33.        .thenComparingInt(s -> s.length()^z)
  34.        .thenComparing(b? Comparator.naturalOrder(): Comparator.reverseOrder());
  35.   }
  36. }
Success #stdin #stdout 0.76s 64900KB
comments (?)
stdin 
Standard input is empty
stdout 
shuffle, all permutations seen after: 14.489 avg
sort, all permutations seen after: 16.429 avg
https://ideone.com/96TWyv
language:
Java (HotSpot 12)
created:
3 years ago
visibility:
secret

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