Algs4-2.2.27子数组长度

 2.2.27子数组长度。用归并将大型随机数组排序，根据经验用N(某次归并时两个子数组的长度之和)的函数估计当一个子数组用尽时另一个子数组的平均长度。

public class E2d2d27
{
    private static Comparable[] aux;
    public static long sumN,subN;
    public static void sort(Comparable[] a)
    {
        sumN=0;
        subN=0;
        aux=new Comparable[a.length];
        sort(a,0,a.length-1);
    }
    public static void sort(Comparable[] a,int lo,int hi)
    {
        if (hi<=lo) return;
        int mid=lo+(hi-lo)/2;
        sort(a,lo,mid);
        sort(a,mid+1,hi);
        merge(a,lo,mid,hi);
    }
   
    public static void merge(Comparable[] a,int lo,int mid,int hi)
    {
        sumN=sumN+(hi-lo+1);
       
        int i=lo,j=mid+1;
        for (int k=lo;k<=hi;k++)
        aux[k]=a[k];
       
        for(int k=lo;k<=hi;k++)
            if        (i>mid) {a[k]=aux[j++];subN++;}
        else if (j>hi)    {a[k]=aux[i++];subN++;}
        else if (less(aux[j],aux[i])) a[k]=aux[j++];
        else            a[k]=aux[i++];
      }
    private static boolean less(Comparable v,Comparable w)
    { return v.compareTo(w)<0;}

     public static boolean isSorted(Comparable[] a)
    {
      for(int i=1;i<a.length;i++)
        if(less(a[i],a[i-1])) return false;
      return true;
    }

      public static void main(String[] args)
     {
         Integer N=Integer.parseInt(args[0]);
         Comparable[] a=new Comparable[N];
         for(int i=0;i<N;i++)
             a[i]=StdRandom.uniform();
         sort(a);
         StdOut.printf("isSorted=%s,N=%d,subN=%d,subN/N=%.4f\n",isSorted(a),sumN,subN,1.0*subN/sumN);
     }
}