void diffarr(int arr[],int n)
{
    int sn=n,index,*ptr=arr;
    int *pfrom=new int[sn];
    for(int i=0;i<sn;i++)
        *(pfrom+i) =i+1 ;
    srand(time(0));
    for(int k=0;k<sn;)
    {
        index=rand()% sn;
        if(*(pfrom+index)!=0)
        {   //從源數據pfrom取，每取一個將其置為0，直至pfrom中所有元素都為0
            *(ptr+k)=pfrom[index];
            pfrom[index]=0;
            k++;
        }
    }
    delete [] pfrom;
}