前言
現在app就是雨后春筍，嗖嗖的往外冒啊，有經驗的、沒經驗的、有資歷的、沒資歷的都想著創業，創業的90%以上都要做一個app出來，好像成了創業的標配。
做了app就得推廣啊，怎么推，發券送錢是最多用的被不可少的了，現在好多產品或者運營都要求能夠隨機出優惠券的金額，但是呢又不能過于隨機，送出去的券都是錢嗎，投資人的錢，是吧。
所以，在隨機生成的金額中就要求，小額度的幾率要大，大額度的幾率要小，比如說3元的70%，5塊的25%，10塊的5%，這個樣子的概率去生成優惠券，這個怎么辦呢？
對于上述的問題，直接用我們的random.next(integer range);就不夠了。因為這個偽隨機不帶權重，3，5，10出現的概率都是一樣的。
實現思路
還是拿上述的例子，3出現的概率是70%，我們給他的權重賦值為70，5出現的概率為25%，我們給他的權重賦值為25，10出現的概率為5%，我們給他的權重賦值為5.
我們按照順序計算出權重的加和，把當前數字出現的權重加和前的值作為其權重范圍的起點值，把加和后的值作為其權重范圍的終點值。
這樣的話，我們就可以使用random.next(100)來做隨機數，然后判斷隨機數落在的范圍，然后映射到對應的優惠券數值即可。
java實現
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package com.nggirl.test.weight.random;import java.util.arraylist;import java.util.hashmap;import java.util.list;import java.util.random;public class weightrandom { public static void main(string[] args){ weightrandom wr = new weightrandom(); wr.initweight(new string[]{ "1","2","3","4" } , new integer[]{ 100,100,200,600 } ); random r = new random(); for (int i = 0; i < 10; i++){ integer rv = r.nextint(wr.getmaxrandomvalue()); system.out.println(rv); system.out.println(wr.getelementbyrandomvalue(rv).getkey() + " " + rv); } hashmap<string, integer> keycount = new hashmap<string, integer>(); keycount.put("1", 0); keycount.put("2", 0); keycount.put("3", 0); keycount.put("4", 0); for (int i = 0; i < 10000; i++){ integer rv = r.nextint(wr.getmaxrandomvalue()); string key = wr.getelementbyrandomvalue(rv).getkey(); keycount.put(key, keycount.get(key).intvalue()+1); } system.out.println(""); } private list<weightelement> weightelements; public void initweight(string[] keys, integer[] weights){ if(keys == null || weights == null || keys.length != weights.length){ return; } weightelements = new arraylist<weightelement>(); for (int i=0; i< keys.length; i++){ weightelements.add(new weightelement(keys[i], weights[i])); } rangeweightelemnts(); printrvs(); } private void rangeweightelemnts(){ if(weightelements.size() == 0){ return; } weightelement ele0 = weightelements.get(0); ele0.setthresholdlow(0); ele0.setthresholdhigh(ele0.getweight()); for (int i = 1; i < weightelements.size(); i++){ weightelement curelement = weightelements.get(i); weightelement preelement = weightelements.get(i - 1); curelement.setthresholdlow(preelement.getthresholdhigh()); curelement.setthresholdhigh(curelement.getthresholdlow() + curelement.getweight()); } } public weightelement getelementbyrandomvalue(integer rv){ //因為元素權重范圍有序遞增，所以這里可以改為二分查找 for (weightelement e:weightelements){ if(rv >= e.getthresholdlow() && rv < e.getthresholdhigh()){ return e; } } return null; } public integer getmaxrandomvalue(){ if(weightelements == null || weightelements.size() == 0){ return null; } return weightelements.get(weightelements.size() - 1).getthresholdhigh(); } public void printrvs(){ for (weightelement e:weightelements){ system.out.println(e.tostring()); } } static class weightelement{ /** * 元素標記 */ private string key; /** * 元素權重 */ private integer weight; /** * 權重對應隨機數范圍低線 */ private integer thresholdlow; /** * 權重對應隨機數范圍高線 */ private integer thresholdhigh; public weightelement(){ } public weightelement(integer weight){ this.key = weight.tostring(); this.weight = weight; } public weightelement(string key, integer weight){ this.key = key; this.weight = weight; } public string getkey() { return key; } public void setkey(string key) { this.key = key; } public integer getweight() { return weight; } public void setweight(integer weight) { this.weight = weight; } public integer getthresholdlow() { return thresholdlow; } public void setthresholdlow(integer thresholdlow) { this.thresholdlow = thresholdlow; } public integer getthresholdhigh() { return thresholdhigh; } public void setthresholdhigh(integer thresholdhigh) { this.thresholdhigh = thresholdhigh; } public string tostring(){ return "key:"+this.key + " weight:" + this.weight + " low:"+this.thresholdlow+" heigh:"+this.thresholdhigh; } }} |
結果：
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2 1028764 876 |
二分法的實現
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public weightelement getelementbyrandomvalue(integer rv){ if(rv < 0 || rv > getmaxrandomvalue()-1){ return null; } //此時rv必然在0 - getmaxrandomvalue()-1范圍內， //也就是必然能夠命中某一個值 int start = 0, end = weightelements.size() - 1; int index = weightelements.size()/2; while(true){ if(rv < weightelements.get(index).getthresholdlow()){ end = index - 1; } else if(rv >= weightelements.get(index).getthresholdhigh()){ start = index + 1; } else{ return weightelements.get(index); } index = (start + end)/2; }} |
下面再分享一則實例，加強對權重隨機算法的理解，一次到位！
權重隨機算法在抽獎，資源調度等系統中應用還是比較廣泛的，一個簡單的按照權重來隨機的實現，權重為幾個隨機對象(分類)的命中的比例，權重設置越高命中越容易，之和可以不等于100；
簡單實現代碼如下：
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import java.util.arraylist;import java.util.list;import java.util.random;public class weightrandom { static list<weightcategory> categorys = new arraylist<weightcategory>(); private static random random = new random(); public static void initdata() { weightcategory wc1 = new weightcategory("a",60); weightcategory wc2 = new weightcategory("b",20); weightcategory wc3 = new weightcategory("c",20); categorys.add(wc1); categorys.add(wc2); categorys.add(wc3); } public static void main(string[] args) { initdata(); integer weightsum = 0; for (weightcategory wc : categorys) { weightsum += wc.getweight(); } if (weightsum <= 0) { system.err.println("error: weightsum=" + weightsum.tostring()); return; } integer n = random.nextint(weightsum); // n in [0, weightsum) integer m = 0; for (weightcategory wc : categorys) { if (m <= n && n < m + wc.getweight()) { system.out.println("this random category is "+wc.getcategory()); break; } m += wc.getweight(); } }}class weightcategory { private string category; private integer weight; public weightcategory() { super(); } public weightcategory(string category, integer weight) { super(); this.setcategory(category); this.setweight(weight); } public integer getweight() { return weight; } public void setweight(integer weight) { this.weight = weight; } public string getcategory() { return category; } public void setcategory(string category) { this.category = category; }} |
結果：
總結
以上就是本文關于java語言實現權重隨機算法完整實例的全部內容，希望對大家有所幫助。如有不足之處，歡迎留言指出。感謝朋友們對本站的支持！
原文鏈接：http://blog.csdn.net/BuquTianya/article/details/51051672
