基本算法描述如下:
1、每个广告增加权重
2、将所有匹配广告的权重相加sum，
3、以相加结果为随机数的种子，生成1~sum之间的随机数rd
4、.接着遍历所有广告，访问顺序可以随意.将当前节点的权重值加上前面访问的各节点权重值得curWt,判断curWt >= rd,如果条件成立则返回当前节点,如果不是则继续累加下一节点. 直到符合上面的条件,由于rd<=sum 因此一定存在curWt>=rd。
特别说明：
此算法和广告的顺序无关
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
public class Test {
/**
* @param args
*/
@SuppressWarnings("unchecked")
public static void main(String[] args) {
List<Node> arrNodes = new ArrayList<Node>();
Node n = new Node(10, "测试1");
arrNodes.add(n);
n = new Node(20, "测试2");
arrNodes.add(n);
n = new Node(30, "测试3");
arrNodes.add(n);
n = new Node(40, "测试4");
arrNodes.add(n);
//Collections.sort(arrNodes, new Node());
Map<String, Integer> showMap = null;
int sum = getSum(arrNodes);
int random = 0;
Node kw = null;
for(int k = 0; k < 20; k++) {
showMap = new LinkedHashMap<String, Integer>();
for(int i = 0; i < 100; i++) {
random = getRandom(sum);
kw = getKW(arrNodes, random);
if(showMap.containsKey(kw.kw)) {
showMap.put(kw.kw, showMap.get(kw.kw) + 1);
} else {
showMap.put(kw.kw, 1);
}
//System.out.println(i + " " +random + " " + getKW(arrNodes, random));
}
System.out.print(k + " ");
System.out.println(showMap);
}
}
public static Node getKW(List<Node> nodes, int rd) {
Node ret = null;
int curWt = 0;
for(Node n : nodes){
curWt += n.weight;
if(curWt >= rd) {
ret = n;
break;
}
}
return ret;
}
public static int getSum(List<Node> nodes) {
int sum = 0;
for(Node n : nodes)
sum += n.weight;
return sum;
}
public static int getRandom(int seed) {
return (int)Math.round(Math.random() * seed);
}
}
class Node implements Comparator{
int weight = 0;
String kw = "";
public Node() {}
public Node(int wt, String kw) {
this.weight = wt;
this.kw = kw;
}
public String toString(){
StringBuilder sbBuilder = new StringBuilder();
sbBuilder.append(" weight=").append(weight);
sbBuilder.append(" kw").append(kw);
return sbBuilder.toString();
}
public int compare(Object o1, Object o2) {
Node n1 = (Node)o1;
Node n2 = (Node)o2;
if(n1.weight > n2.weight)
return 1;
else
return 0;
}
}