Created
February 1, 2021 09:19
-
-
Save Taskeren/1db8fd362c81dcda92c985dd5ce4d5e8 to your computer and use it in GitHub Desktop.
加权随机数 Weighted Random
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| package testified; | |
| import com.google.common.collect.Lists; | |
| import com.google.common.collect.Maps; | |
| import java.util.List; | |
| import java.util.Map; | |
| import java.util.Map.Entry; | |
| import java.util.Random; | |
| public class WeightRandom<V> { | |
| private final Random rand; | |
| /** 元素池，随机出来指针后从这里提取元素 */ | |
| private final List<V> pool = Lists.newArrayList(); | |
| /** 加权最大值 */ | |
| private int cap = 0; | |
| /** 加权元素池（元素指针，元素加权值） */ | |
| private final Map<Integer, Integer> caps = Maps.newHashMap(); | |
| public WeightRandom() { | |
| this(new Random()); | |
| } | |
| public WeightRandom(Random rand) { | |
| this.rand = rand; | |
| } | |
| public void add(int weight, V element) { | |
| pool.add(element); // 放到元素池里 | |
| caps.put(pool.size()-1, cap+weight); // 放到加权元素池里 | |
| cap += weight; // 更新最大加权值 | |
| } | |
| public V next() { | |
| final int rind = rand.nextInt(cap); // 随机一个加权值 | |
| for(Entry<Integer, Integer> entry : caps.entrySet()) { // 找到刚好比随机加权值小的元素指针 | |
| final int ind = entry.getKey(); | |
| final int cap = entry.getValue(); | |
| if(cap > rind) { | |
| return pool.get(ind); | |
| } | |
| } | |
| throw new IllegalStateException("unexpected"); | |
| } | |
| public String toString() { | |
| StringBuilder sb = new StringBuilder("WeightRandom{ "); | |
| caps.forEach( (index, cap) -> { | |
| final V content = pool.get(index); | |
| sb.append(String.valueOf(content)).append("=").append(cap).append(" "); | |
| }); | |
| sb.append("}"); | |
| return sb.toString(); | |
| } | |
| } |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment