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java语言实现权重随机算法完整实例

时间:2021-02-22 11:35     来源/作者:buqutianya

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。

java语言实现权重随机算法完整实例

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

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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:

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2 102
876
4 876

二分法的实现

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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;

java语言实现权重随机算法完整实例

简单实现代码如下:

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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:

java语言实现权重随机算法完整实例

总结

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原文链接:http://blog.csdn.net/BuquTianya/article/details/51051672

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