【Java实现】带权重的随机数算法
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(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。
import*;
public class WeightRandom {
private List<WeightElement> weightElements;
public void initWeight(String[] keys, Integer[] weights){
if(keys ==null|| weights ==null|| keys.length != weights.length){//异常传参情况
return;
}
weightElements =new ArrayList<>();
for(int i=0; i< keys.length; i++){
weightElements.add(new WeightElement(keys[i], weights[i]));
}
if(weightElements.size()==0){
return;
}
//初始化后分配各个key中的元素值
WeightElement ele0 = (0);
ele0.setThresholdLow(0);
ele0.Weight());
for(int i =1; i < weightElements.size(); i++){
WeightElement curElement = (i);
WeightElement preElement = (i -1);
curElement.ThresholdHigh());
curElement.ThresholdLow()+ Weight());
}
}
//⼆分查写法
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 < (index).getThresholdLow()){
end = index -1;
}else if(rv >= (index).getThresholdHigh()){
start = index +1;
}else{
(index);
}
index =(start + end)/2;
}
}
/**⾮⼆分查的写法
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
for (WeightElement e:weightElements){
if(rv >= e.getThresholdLow() && rv < e.getThresholdHigh()){
return e;
}
}
return null;
}**/
public int getMaxRandomValue(){
if(weightElements ==null|| weightElements.size()==0){
return0;
(weightElements.size()-1).getThresholdHigh();
}
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下限和上限
private Integer thresholdLow;
private Integer thresholdHigh;
public WeightElement(String key, Integer weight){
this.key = key;
this.weight = weight;
}
public String getKey(){
return key;
}
java生成随机数的方法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 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.MaxRandomValue());
System.out.println(rv);
System.out.ElementByRandomValue(rv).getKey()+" "+ rv);
}
//针对随机到的元素个数做⼀个简单测试
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.MaxRandomValue());
String key = wr.getElementByRandomValue(rv).getKey();
keyCount.put(key, (key)+1);
}
System.out.println(keyCount);
System.out.println("");
}
}
```
结果：{1=1018,2=1008,3=2081,4=5893}

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