本文實(shí)例講述了Java權(quán)重隨機(jī)的實(shí)現(xiàn)方法。分享給大家供大家參考。具體分析如下:
權(quán)重隨機(jī)在項(xiàng)目中經(jīng)常用到,所以我把它抽象到一個(gè)工具類中。
一般實(shí)現(xiàn)隨機(jī)權(quán)重有兩種方式:
1. 使用一個(gè)數(shù)組存放權(quán)重對(duì)應(yīng)的實(shí)際目標(biāo),比如A的權(quán)重是2,B的權(quán)重是3,那么數(shù)組長度為5, 數(shù)組前兩個(gè)存放A,后三個(gè)存放B。
然后隨機(jī)一個(gè)[0-數(shù)據(jù)長度)的數(shù)字,直接取數(shù)組對(duì)應(yīng)下標(biāo)的值就可以了。
優(yōu)點(diǎn):數(shù)據(jù)結(jié)構(gòu)簡單,算法高效,實(shí)現(xiàn)簡單
缺點(diǎn):當(dāng)權(quán)重值比較大同時(shí)數(shù)據(jù)又比較多的時(shí)候,會(huì)浪費(fèi)內(nèi)存
2. 使用區(qū)間算法,從前到后依次疊加權(quán)重,然后隨機(jī)一個(gè)[1-權(quán)重和]的數(shù)字,再用隨機(jī)的權(quán)重依次減去每個(gè)元素的權(quán)重,當(dāng)?shù)谝粋€(gè)小于等于0的元素就是我們找元素
這里實(shí)現(xiàn)可以借用Arrays的binarySearch方法。
完整實(shí)例代碼點(diǎn)擊此處本站下載。
貼一下代碼:
WeightMeta.java:
/**
* 建議使用RandomUtil類創(chuàng)建RandomMeta對(duì)象
* @author wxf on 14-5-5.
*/
public class WeightMeta<T> {
private final Random ran = new Random();
private final T[] nodes;
private final int[] weights;
private final int maxW;
public WeightMeta(T[] nodes, int[] weights) {
this.nodes = nodes;
this.weights = weights;
this.maxW = weights[weights.length - 1];
}
/**
* 該方法返回權(quán)重隨機(jī)對(duì)象
* @return
*/
public T random() {
int index = Arrays.binarySearch(weights, ran.nextInt(maxW) + 1);
if (index < 0) {
index = -1 - index;
}
return nodes[index];
}
public T random(int ranInt) {
if (ranInt > maxW) {
ranInt = maxW;
} else if(ranInt < 0){
ranInt = 1;
} else {
ranInt ++;
}
int index = Arrays.binarySearch(weights, ranInt);
if (index < 0) {
index = -1 - index;
}
return nodes[index];
}
@Override
public String toString() {
StringBuilder l1 = new StringBuilder();
StringBuilder l2 = new StringBuilder("[random]/t");
StringBuilder l3 = new StringBuilder("[node]/t/t");
l1.append(this.getClass().getName()).append(":").append(this.hashCode()).append(":/n").append("[index]/t/t");
for (int i = 0; i < weights.length; i++) {
l1.append(i).append("/t");
l2.append(weights[i]).append("/t");
l3.append(nodes[i]).append("/t");
}
l1.append("/n");
l2.append("/n");
l3.append("/n");
return l1.append(l2).append(l3).toString();
}
}
RandomUtil.java:
/**
* 隨機(jī)工具類
*
* 使用權(quán)重的集合Map構(gòu)建隨機(jī)元數(shù)據(jù)對(duì)象
*
* 比如:
* 我們有3個(gè)url地址,他們的權(quán)重分別為1,2,3現(xiàn)在我們利用RandomUtil來根據(jù)權(quán)重隨機(jī)獲取url:
*
* <p><blockquote><pre>
*
* map.put(url1, 1);
* map.put(url2, 2);
* map.put(url3, 3);
* RandomMeta<String, Integer> md = RandomUtil.buildWeightMeta(map);
* String weightRandomUrl = md.random();
*
* </pre></blockquote><p>
*
* @author wxf on 14-5-5.
*/
public class RandomUtil {
public static <T> WeightMeta<T> buildWeightMeta(final Map<T, Integer> weightMap) {
final int size = weightMap.size();
Object[] nodes = new Object[size];
int[] weights = new int[size];
int index = 0;
int weightAdder = 0;
for (Map.Entry<T, Integer> each : weightMap.entrySet()) {
nodes[index] = each.getKey();
weights[index++] = (weightAdder = weightAdder + each.getValue());
}
return new WeightMeta<T>((T[]) nodes, weights);
}
}
希望本文所述對(duì)大家的Java程序設(shè)計(jì)有所幫助。