二路归并排序

二路归并排序

算法思想是每次把待排序列分成两部分，分别对这两部分递归地用归并排序，完成后把这两个子部分合并成一个
序列。

import  java.lang.reflect.Array;
public   class  MergeSorter < E  extends  Comparable < E >>   extends  Sorter < E > {
    @SuppressWarnings( " unchecked " )
    @Override
     public   void  sort(E[] array,  int  from,  int  len){
         if (len <= 1 )  return ;
        E[] temporary = (E[])Array.newInstance(array[ 0 ].getClass(),len);
        merge_sort(array,from,from + len - 1 ,temporary);
    }
     private   final   void  merge_sort(E[] array,  int  from,  int  to,E[] temporary){
         if (to <= from)  return ;
         int  middle = (from + to) / 2 ;
        merge_sort(array,from,middle,temporary);
        merge_sort(array,middle + 1 ,to,temporary);
        merge(array,to,middle,temporary);
    }
     private   final   void  merge(E[] array,  int  from,  int  to,  int  middle,E[] temporary){
         int  k = 0 , leftIndex = 0 ,rightIndex = to - from;
        System.arraycopy(array,from,temporary, 0 ,middle - from + 1 );
         for ( int  i = 0 ;i < to - middle;i ++ ){
            temporary[to - from - i] = array[middle + i + 1 ];
        }
         while (k < to - from + 1 ){
             if (temporary[leftIndex].compareTo(temporary[rightIndex]) < 0 ){
                array[k + from] = temporary[leftIndex ++ ];
            } else {
                array[k + from] = temporary[rightIndex -- ];
            }
            k ++ ;
        }
    }
}