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; } }