content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you under the Apache License, Version 2.0 (the
   * "License"); you may not use this file except in compliance
   * with the License.  You may obtain a copy of the License at
   *
   *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing,
   * software distributed under the License is distributed on an
   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   * KIND, either express or implied.  See the License for the
   * specific language governing permissions and limitations
   * under the License.
   */
  
  package org.apache.bifromq.basecluster.util;
  
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.List;
  import java.util.concurrent.ThreadLocalRandom;
  import java.util.function.Predicate;
  import java.util.stream.Collectors;
  
  public class RandomUtils {
      public static <T> List<T> uniqueRandomPickAtMost(List<T> list, int max, Predicate<T> predicate) {
          int n = list.size();
          if (n <= max) {
              return list.stream().filter(predicate).collect(Collectors.toList());
          } else {
              HashMap<Integer, Integer> hash = new HashMap<>(2 * max);
              int[] offsets = new int[max];
              for (int i = 0; i < max; i++) {
                  int j = i + ThreadLocalRandom.current().nextInt(n - i);
                  offsets[i] = (hash.containsKey(j) ? hash.remove(j) : j);
                  if (j > i) {
                      hash.put(j, (hash.containsKey(i) ? hash.remove(i) : i));
                  }
              }
              List<T> randSelected = new ArrayList<>();
              for (int i : offsets) {
                  T peer = list.get(i);
                  if (predicate.test(peer)) {
                      randSelected.add(peer);
                  }
              }
              return randSelected;
          }
      }
  }
  