Java版的堆排、快排、筛法

转自  -  小媛在努力

原文： http://blog.csdn.net/zxy_snow/article/details/6240868
 

堆排

 

import java.io.*;
import java.util.*;
public class HeapSort{
public static void heapMin(int a[],int i,int heapsize)
{
int tmp,larg;
int lchild = i<<1,rchild = lchild+1;
if( lchild <= heapsize && a[lchild] > a[i] )
larg = lchild;
else
larg = i;
if( rchild <= heapsize && a[rchild] > a[larg] )
larg = rchild;
if( larg != i )
{
tmp = a[i];
a[i] = a[larg];
a[larg] = tmp;
heapMin(a,larg,heapsize);
}
}
public static void Heapsort(int a[],int n)
{
int heapsize = n;
for(int i=n>>1; i>=1; i--)
heapMin(a,i,n);
for(int i=n; i>=2; i--)
{
int tmp;
tmp = a[i];
a[i] = a[1];
a[1] = tmp;
heapsize--;
heapMin(a,1,heapsize);
}
}
public static void main(String args[])
{
Scanner cin = new Scanner(System.in);
int n = cin.nextInt();
int a[] = new int[50];
for(int i=1; i<=n; i++)
a[i] = cin.nextInt();
Heapsort(a,n);
for(int i=1; i<=n; i++)
System.out.print( a[i] + " " );
}
}

 

快排

 import java.io.*;
import java.util.*;
public class Qsort{

public static int partition(int a[],int p,int r){
int i = p-1;
int x = a[r];
int tmp;
for(int j=p; j<r; j++)
if( a[j] <= x )
{
i++;
tmp = a[i];
a[i] = a[j];
a[j] = tmp;
}
tmp = a[i+1];
a[i+1] = a[r];
a[r] = tmp;
return i+1;
}

public static void qsort(int a[],int p,int r){
if( p < r )
{
int q = partition(a,p,r);
qsort(a,p,q-1);
qsort(a,q+1,r);
}
}

public static void main(String args[]){
int a[] = new int[50];
int n;
Scanner cin = new Scanner(System.in);
n = cin.nextInt();
int i;
for(i=1; i<=n; i++)
a[i] = cin.nextInt();
qsort(a,1,n);
for(i=1; i<=n; i++)
System.out.print( "" + ' ' + a[i] );
}
}

 

筛法

 public class shaifa{
public static int MAX = 1000001;
public static int a[] = new int[MAX];
public static void init(){
int i,j;
for(i=1; i<MAX; i++)
a[i] = 1;
a[0] = a[1] = 0;
for(i=2; i<MAX; i++)
for(j=2; j*i<MAX; j++)
if( a[i] == 1 )
a[j*i] = 0;
for(i=1; i<MAX; i++)
if( a[i] == 1 )
System.out.print(i+""+' ');
}
public static void main(String args[]){
init();
}
}