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 1028764 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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