权重算法实现（转）

原文地址：http://www.blogjava.net/willpower88/archive/2010/08/31/330437.html
需求：广告按权重展现

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;
    }
}