Weight algorithm

Weight.java

/**
 * $Id: WeightUtil.java 406 2012-08-14 07:44:42Z xiaowei.hu $
 * Copyright 2012-2014 Oak Pacific Interactive. All rights reserved.
 */
package com.renren.socialgame.kp.util;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;

/**
 * 权重util
 * 
 * @author <a href="mailto:xiaowei.hu@renren-inc.com">Xiaowei Hu</a>
 * @version 1.0 2012-8-14 下午03:07:57
 * @since 1.0
 */
public class WeightUtil {
    public static interface WeightObject<T> {
        int getWeight(T t);
    }
    
    /**
     * 通过权重值获取对象
     * 
     * @param <T>
     * @param list
     * @param obj
     * @return
     */
    public static <T> T weight(List<T> list, WeightObject<T> obj) {
        List<Integer> weightValue = new ArrayList<Integer>();
        for (T t : list) {
            weightValue.add(obj.getWeight(t));
        }
        return list.get(getIndexByWeight(weightValue));
    }
    

    private static int getIndexByWeight(List<Integer> weight) {
        int count = 0;
        for (int i = 0; i < weight.size(); i++) {
            count += weight.get(i).intValue();
        }

        Random random = new Random();
        int seed = random.nextInt(count) + 1;
        for (int i = 0; i < weight.size(); i++) {

            int preSum = 0;
            for (int j = i; j >= 0; j--) {
                preSum += weight.get(j).intValue();
            }

            if (preSum >= seed) {
                return i;
            }
        }
        return -1;
    }
}