权重值设置问题
一个简单的方法根据权重，按照比例随机显示对应的广告， 权重值越大，概率越大。 比如有个广告list，广告属性有id,weight，写个通用方法来根据权重显示广告id：
public class TEST {
` public`static void main(String[] args) {
` List`new ArrayList<Ad>();
` list.add(`new Ad( 1 , 5 ));
` list.add(`new Ad( 2 , 10 ));
` list.add(`new Ad( 3 , 20 ));
` list.add(`new Ad( 4 , 30 ));
` list.add(`new Ad( 5 , 35 ));
` ComTest com =`new ComTest();
` Collections.sort(list,com);`//对list中广告的权重要先排序，否则无法将随机数顺序安置到对应的区间
` int`id1= 0 ;
` int`id2= 0 ;
` int`id3= 0 ;
` int`id4= 0 ;
` int`id5= 0 ;
` for`( int i = 0 ; i < 100 ; i++) {
` int`id = getAd(list);
` if`(id== 1 ) id1++;
` if`(id== 2 ) id2++;
` if`(id== 3 ) id3++;
` if`(id== 4 ) id4++;
` if`(id== 5 ) id5++;
` } //`
` System.out.println(`"12345:" +id1+ "|" +id2+ "|" +id3+ "|" +id4+ "|" +id5); //统计各id出现的次数
` }`
` public`static int getAd(List<Ad> list){ //根据权重返回对应id的方法
` int`sumWeight = 0 ; //得到总权重
` for`(Ad ad :list){
` sumWeight+=ad.getWeight();`
` }`
` Random rand =`new Random();
` int`x = rand.nextInt(sumWeight) + 1 ; //生成随机数
` int`start = 0 ; int end = 0 ;
` for`( int i= 1 ;i<list.size();i++){
` //计算各个权重对应的起止数值段`
` if`(i== 1 ){
` start = list.get(i-`1 ).getWeight();
` end = list.get(i-`1 ).getWeight()+list.get(i).getWeight();
` }`else {
` start = end;`
` end = start+list.get(i).getWeight();`
` }`
` //根据随机数落入的范围返回对应几率的广告id`
` if`(x>start && x<=end){
` return`list.get(i).getId();
` }`else if (x<=start){
` return`list.get(i- 1 ).getId();
` }`else {
` continue`;
` }`
` }`
` return`0 ;
` }`
}
``
class Ad{
``
` public`Ad( int id, int weight){
` this`.id = id;
` this`.weight = weight;
` }`
` int`id;
` int`weight;
``
` public`int getId() {
` return`id;
` }`
``
` public`void setId( int id) {
` this`.id = id;
` }`
``
` public`int getWeight() {
` return`weight;
` }`
``
` public`void setWeight( int weight) {
` this`.weight = weight;
` }`
``
}
待我称王封你为后i
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