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1 package cn.edu.buaa.randomSelectAlgo; 2  3 /** 4  * 等概率从n个数中随机选取m个数,概率为m/n。适用于数据能一次全读入的场景. 5  *  6  */ 7 public class Main_RamdomSelectAlgo { 8     static int[] data = { 5, 6, 7, 8, 9, 1, 2, 3, 4 }; 9     static int[] selectCount = { 0, 0, 0, 0, 0, 0, 0, 0, 0 };10     static int loopCount = 1000_000;// 测试次数，为1次时打印结果即为选取结果11 12     public static void main(String[] args) {13         // TODO Auto-generated method stub14         for (int i = 0; i < loopCount; i++) {15             randSelect(data, 5);16         }17         for (int i = 0; i < selectCount.length; i++) {18             System.out.print(selectCount[i] + ", ");19         }20     }21 22     static boolean randSelect(int[] data, int selectNum) {23         int nSize = data.length;24         if (nSize < selectNum || selectNum < 0) {25             return false;26         }27         for (int i = 0, iSize = nSize; i < iSize; i++) {
    // 遍历一遍数据28             double tmpRamNum = Math.random();29             if (tmpRamNum <= (double) selectNum / nSize) {30                 // data[i] is selected31                 selectCount[i]++;// 被选数被选次数加1，初始为032                 selectNum--;33             }34             nSize--;35         }36         return true;37     }38 }

 

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