权重随机算法(java 版)

应用场景：

游戏里面随机抽奖 ，根据权重随机。

代码如下：

/**
* 权重随机（效率佳）
* 200003|200004|200005|200005
4000|2000|1000|500
*
4000/7500
* map
*
*0----500---1000-------2000-------4000
*/
public static int random(Map<String ,String> map){
Set<Map.Entry<String, String>> entries = map.entrySet();
Random random = new Random();
int sum=0;
for (Map.Entry<String, String> entry : entries) {
String value = entry.getValue();
int valueInt = Integer.parseInt(value);
sum+=valueInt;
}
int randomInt = random.nextInt(sum)+1;
int sum_temp = 0;
for (Map.Entry<String, String> entry : entries) {
String value = entry.getValue();
int valueInt = Integer.parseInt(value);
sum_temp += valueInt;
if (randomInt <= sum_temp)
{
return Integer.parseInt(entry.getKey());
}
}
return -1;
}
// 按照权重随机（效率不太好）
public static String weightRandom(Map<String, String> map) {
Set<String> keySet = map.keySet();
List<String> weights = new ArrayList<String>();
for (Iterator<String> it = keySet.iterator(); it.hasNext();) {
String weightStr = it.next();//key
int weight = Integer.valueOf(map.get(weightStr));
for (int i = 0; i <= weight; i++) {
weights.add(weightStr);
}
}
Random random = new Random();
int idx = random.nextInt(weights.size());
return weights.get(idx);
}

测试：

public static void main(String[] args) {

Map map=new HashMap<String,String>();
//200003|200004|200005|200006
4000|2000|1000|500
map.put("200003","40");
map.put("200004","30");
map.put("200005","20");
map.put("200006","10");
int sum200003=0;
int sum200004=0;
int sum200005=0;
int sum200006=0;
for (int i = 0; i < 1000; i++) {
int random = random(map);
//
String randomStr = weightRandom(map);
//
int random = Integer.parseInt(randomStr);
if(random==200003){
sum200003++;
}
if(random==200004){
sum200004++;
}
if(random==200005){
sum200005++;
}
if(random==200006){
sum200006++;
}
}
System.out.println("sum200003:"+sum200003);
System.out.println("sum200004:"+sum200004);
System.out.println("sum200005:"+sum200005);
System.out.println("sum200006:"+sum200006);

}

最后

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