33,027
社区成员




#include<iostream.h>
#include<stdlib.h>
#include<time.h>
#define MAX_VALUE 10000
#define random() rand()%MAX_VALUE
#define N 10000
int a[N];
class Find
{
public:
void bubble(int first,int end) //冒泡排序
{
for(int flag=first;flag<end;flag++)
for(int i=end;i>flag;i--)
if(a[i]<a[i-1])
{ int t=a[i];
a[i]=a[i-1];
a[i-1]=t;
}
}
int partition(int p,int r,int x) //数组a中从a[p]到a[r]的元素按照x划分,大于x的在左边,小于x的在右边
{
int i,j;
for(i=p,j=r;i<j;i++)
{
if(a[i]>x)
{
while(i<j&&a[j]>x)
j--;
if(i!=j){
int t=a[i];
a[i]=a[j];
a[j]=t;
j--;
}
}
}
return i-1;
}
int select(int p,int r,int k) //寻找中位数
{
if(r-p<5){
bubble(p,r);
return a[p+k-1];
}
for(int i=0;i<(r-p-4)/5;i++)
{
int s=p+5*i,t=s+4;
bubble(s,t);
int temp=a[p+i];
a[p+i]=a[s+2];
a[s+2]=temp;
}
int x=select(p,p+(r-p-4)/5,(r-p+6)/10);
i=partition(p,r,x);
int j=i-p+1;
if(k<=j)
return select(p,i,k);
else
return select(i+1,r,k-j);
}
};
void main()
{
clock_t start,end;
double elapsed;
srand((int)time(NULL));
for(int k=0;k<N;k++)
{
a[k]=random();
cout<<a[k]<<"\t";
}
cout<<endl;
start=clock();
Find f;
int n=5000;
cout<<"The No."<<n<<" is :"<<f.select(0,N-1,n)<<endl;
end=clock();
elapsed=((double)(end-start));///CLOCKS_PER_SEC;
cout<<"Time: "<<elapsed<<endl;
}