/*
* 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 openbook.util;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Random;
import java.util.Set;
/**
* A set of static utility functions for simulating pseudo-randomness.
*
* @author Pinaki Poddar
*
*/
public class Randomizer {
private static final Random rng = new Random(System.currentTimeMillis());
private static final int MIN_ALPHA = (int)'A';
private static final int MAX_ALPHA = (int)'Z';
/**
* Returns true with a probability of p.
*/
public static boolean probability(double p) {
return rng.nextDouble() < p;
}
/**
* Picks a random number between 0 (inclusive) and N (exclusive).
*/
public static int random(int n) {
return rng.nextInt(n);
}
/**
* Picks a uniformly distributed random integer within the given range.
*/
public static int random(int min, int max) {
return min + rng.nextInt(max-min);
}
public static double random(double min, double max) {
return min + rng.nextDouble()*(max-min);
}
/**
* Generates a random alphanumeric String with each segment separated by a dash.
*/
public static String randomString(int...segments) {
StringBuilder tmp = new StringBuilder();
for (int s : segments) {
tmp.append(tmp.length() == 0 ? (char)random(MIN_ALPHA, MAX_ALPHA) : '-');
for (int j = 0; j < s; j++)
tmp.append(random(10));
}
return tmp.toString();
}
/**
* Picks a random element from the given list.
*/
public static <T> T selectRandom(List<T> list) {
if (list == null || list.isEmpty())
return null;
if (list.size() == 1)
return list.get(0);
return list.get(random(list.size()));
}
/**
* Selects n elements randomly from the given list.
*/
public static <T> List<T> selectRandom(List<T> list, int n) {
if (list == null || list.isEmpty())
return Collections.emptyList();
Set<Integer> indices = new HashSet<Integer>();
List<T> selected = new ArrayList<T>();
int m = list.size();
if (n >= m) {
selected.addAll(list);
} else {
while (indices.size() < n) {
indices.add(random(m));
}
for (Integer index : indices) {
selected.add(list.get(index));
}
}
return selected;
}
}