权重随机抽取

[1].[代码] [Java]代码 跳至 [1]

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import java.math.BigDecimal; import java.util.HashMap; import java.util.Map;   import org.apache.commons.collections.Bag; import org.apache.commons.collections.bag.TreeBag;   /**   * 按照权重随机抽取元素   * @author heyang   *   */ public class RandomUtil {      /**       * 根据指定的样本数组和样本-权重映射随机抽取一个元素       * @param elementArray 样本数组       * @param weightMap 样本-权重映射       * @return       * @throws Exception       */      public static Object randomByWeight(Object[] elementArray,Map<Object,Integer> weightMap) throws Exception{          if (elementArray== null ||elementArray.length== 0 ){              throw new Exception( "ElementArray must not be empty!" );          }          if (weightMap== null || weightMap.isEmpty()){              throw new Exception( "WeightMap must not be empty!" );          }          int [] weightArray = new int [elementArray.length+ 1 ];          Object[] tempElementArray = new Object[elementArray.length];          for ( int i= 0 ;i<elementArray.length;i++){              tempElementArray[i] = elementArray[i];              Integer weight = weightMap.get(elementArray[i]);              weightArray[i+ 1 ] = weight+weightArray[i];          }          double randomNum = weightArray[weightArray.length- 1 ]*Math.random();          int index = bidSearch(weightArray,randomNum);          return index==- 1 ? null :tempElementArray[index];      }            private static int bidSearch( int [] desArray, double des){          int low = 0 ;          int high = desArray.length- 1 ;            while (low <= high) {              int middle = (low + high)/ 2 ;                if (des > desArray[middle] && des<=desArray[middle+ 1 ]) {                    return middle;              } else if (des <desArray[middle]) {                    high = middle - 1 ;                } else {                    low = middle + 1 ;                }           }           return - 1 ;      }            public static void main(String[] args) throws Exception{          String[] a = { "a" , "b" , "c" , "d" , "e" };          Map<Object,Integer> b = new HashMap<Object, Integer>();          b.put( "a" , 12 );          b.put( "b" , 11 );          b.put( "c" , 0 );          b.put( "d" , 19 );          b.put( "e" , 0 );          b.put( "f" , 20 );          int total = 0 ;          for (Object x:a){              int c = b.get(x);              total+=c;          }          for (Object x:a){              BigDecimal percent = new BigDecimal(b.get(x)).divide( new BigDecimal(total), 8 ,BigDecimal.ROUND_HALF_EVEN);              System.out.println( "Element:" +x+ "\tpercent:" + percent.toString());          }          Bag bag = new TreeBag();          for ( int i= 0 ;i< 1000000 ;i++){              Object res = randomByWeight(a,b);              bag.add(res);          }          for (Object x:a){              System.out.println( "Element:" +x+ "\tcount:" +bag.getCount(x));          }                } }