java语言实现权重随机算法完整实例

前言

现在app就是雨后春笋，嗖嗖的往外冒啊，有经验的、没经验的、有资历的、没资历的都想着创业，创业的90%以上都要做一个app出来，好像成了创业的标配。

做了app就得推广啊，怎么推，发券送钱是最多用的被不可少的了，现在好多产品或者运营都要求能够随机出优惠券的金额，但是呢又不能过于随机，送出去的券都是钱吗，投资人的钱，是吧。

所以，在随机生成的金额中就要求，小额度的几率要大，大额度的几率要小，比如说3元的70%，5块的25%，10块的5%，这个样子的概率去生成优惠券，这个怎么办呢？

对于上述的问题，直接用我们的Random.next(Integer range);就不够了。因为这个伪随机不带权重，3，5，10出现的概率都是一样的。

实现思路

还是拿上述的例子，3出现的概率是70%，我们给他的权重赋值为70，5出现的概率为25%，我们给他的权重赋值为25，10出现的概率为5%，我们给他的权重赋值为5.

我们按照顺序计算出权重的加和，把当前数字出现的权重加和前的值作为其权重范围的起点值，把加和后的值作为其权重范围的终点值。

这样的话，我们就可以使用Random.next(100)来做随机数，然后判断随机数落在的范围，然后映射到对应的优惠券数值即可。

java实现

package com.nggirl.test.weight.random;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Random;
public class WeightRandom {
	public static void main(String[] args){
		WeightRandom wr = new WeightRandom();
		wr.initWeight(new String[]{
			"1","2","3","4"
		}
		, new Integer[]{
			100,100,200,600
		}
		);
		Random r = new Random();
		for (int i = 0; i < 10; i++){
			Integer rv = r.nextint(wr.getMaxRandomValue());
			System.out.println(rv);
			System.out.println(wr.getElementByRandomValue(rv).getKey() + " " + rv);
		}
		HashMap<String, Integer> keyCount = new HashMap<String, Integer>();
		keyCount.put("1", 0);
		keyCount.put("2", 0);
		keyCount.put("3", 0);
		keyCount.put("4", 0);
		for (int i = 0; i < 10000; i++){
			Integer rv = r.nextint(wr.getMaxRandomValue());
			String key = wr.getElementByRandomValue(rv).getKey();
			keyCount.put(key, keyCount.get(key).intValue()+1);
		}
		System.out.println("");
	}
	private List<WeightElement> weightElements;
	public void initWeight(String[] keys, Integer[] weights){
		if(keys == null || weights == null || keys.length != weights.length){
			return;
		}
		weightElements = new ArrayList<WeightElement>();
		for (int i=0; i< keys.length; i++){
			weightElements.add(new WeightElement(keys[i], weights[i]));
		}
		rangeWeightElemnts();
		printRvs();
	}
	private void rangeWeightElemnts(){
		if(weightElements.size() == 0){
			return;
		}
		WeightElement ele0 = weightElements.get(0);
		ele0.setThresholdLow(0);
		ele0.setThresholdHigh(ele0.getWeight());
		for (int i = 1; i < weightElements.size(); i++){
			WeightElement curElement = weightElements.get(i);
			WeightElement preElement = weightElements.get(i - 1);
			curElement.setThresholdLow(preElement.getThresholdHigh());
			curElement.setThresholdHigh(curElement.getThresholdLow() + curElement.getWeight());
		}
	}
	public WeightElement getElementByRandomValue(Integer rv){
		//因为元素权重范围有序递增，所以这里可以改为二分查找
		for (WeightElement e:weightElements){
			if(rv >= e.getThresholdLow() && rv < e.getThresholdHigh()){
				return e;
			}
		}
		return null;
	}
	public Integer getMaxRandomValue(){
		if(weightElements == null || weightElements.size() == 0){
			return null;
		}
		return weightElements.get(weightElements.size() - 1).getThresholdHigh();
	}
	public void printRvs(){
		for (WeightElement e:weightElements){
			System.out.println(e.toString());
		}
	}
	static class WeightElement{
		/**
     * 元素标记
     */
		private String key;
		/**
     * 元素权重
     */
		private Integer weight;
		/**
     * 权重对应随机数范围低线
     */
		private Integer thresholdLow;
		/**
     * 权重对应随机数范围高线
     */
		private Integer thresholdHigh;
		public WeightElement(){
		}
		public WeightElement(Integer weight){
			this.key = weight.toString();
			this.weight = weight;
		}
		public WeightElement(String key, Integer weight){
			this.key = key;
			this.weight = weight;
		}
		public String getKey() {
			return key;
		}
		public void setKey(String key) {
			this.key = key;
		}
		public Integer getWeight() {
			return weight;
		}
		public void setWeight(Integer weight) {
			this.weight = weight;
		}
		public Integer getThresholdLow() {
			return thresholdLow;
		}
		public void setThresholdLow(Integer thresholdLow) {
			this.thresholdLow = thresholdLow;
		}
		public Integer getThresholdHigh() {
			return thresholdHigh;
		}
		public void setThresholdHigh(Integer thresholdHigh) {
			this.thresholdHigh = thresholdHigh;
		}
		public String toString(){
			return "key:"+this.key + " weight:" + this.weight + " low:"+this.thresholdLow+" heigh:"+this.thresholdHigh;
		}
	}
}

结果：

2 102
876
4 876

二分法的实现

public WeightElement getElementByRandomValue(Integer rv){
	if(rv < 0 || rv > getMaxRandomValue()-1){
		return null;
	}
	//此时rv必然在0 - getMaxRandomValue()-1范围内，
	//也就是必然能够命中某一个值
	int start = 0, end = weightElements.size() - 1;
	int index = weightElements.size()/2;
	while(true){
		if(rv < weightElements.get(index).getThresholdLow()){
			end = index - 1;
		} else if(rv >= weightElements.get(index).getThresholdHigh()){
			start = index + 1;
		} else{
			return weightElements.get(index);
		}
		index = (start + end)/2;
	}
}

下面再分享一则实例，加强对权重随机算法的理解，一次到位！

权重随机算法在抽奖，资源调度等系统中应用还是比较广泛的，一个简单的按照权重来随机的实现，权重为几个随机对象(分类)的命中的比例，权重设置越高命中越容易，之和可以不等于100；

简单实现代码如下：

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
public class WeightRandom {
	static List<WeightCategory> categorys = new ArrayList<WeightCategory>();
	private static Random random = new Random();
	public static void initData() {
		WeightCategory wc1 = new WeightCategory("A",60);
		WeightCategory wc2 = new WeightCategory("B",20);
		WeightCategory wc3 = new WeightCategory("C",20);
		categorys.add(wc1);
		categorys.add(wc2);
		categorys.add(wc3);
	}
	public static void main(String[] args) {
		initData();
		Integer weightSum = 0;
		for (WeightCategory wc : categorys) {
			weightSum += wc.getWeight();
		}
		if (weightSum <= 0) {
			System.err.println("Error: weightSum=" + weightSum.toString());
			return;
		}
		Integer n = random.nextint(weightSum);
		// n in [0, weightSum)
		Integer m = 0;
		for (WeightCategory wc : categorys) {
			if (m <= n && n < m + wc.getWeight()) {
				System.out.println("This Random Category is "+wc.getCategory());
				break;
			}
			m += wc.getWeight();
		}
	}
}
class WeightCategory {
	private String category;
	private Integer weight;
	public WeightCategory() {
		super();
	}
	public WeightCategory(String category, Integer weight) {
		super();
		this.setCategory(category);
		this.setWeight(weight);
	}
	public Integer getWeight() {
		return weight;
	}
	public void setWeight(Integer weight) {
		this.weight = weight;
	}
	public String getCategory() {
		return category;
	}
	public void setCategory(String category) {
		this.category = category;
	}
}

结果：

总结

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