快排之一

//递归实现快排

#include <iostream>
using namespace std;
int arr[1000];
int part(int beg, int end)
{
    int low=beg,high=end;
    int pivot=arr[beg];
    while(low<high)
    {
        while(low<high && arr[high]>=pivot)
            --high;
        arr[low]=arr[high];
        while(low<high && arr[low]<=pivot)
            ++low;
        arr[high]=arr[low];
    }
    arr[low]=pivot;    //low=high
    return low;
}
void QuickSort(int beg,int end)
{
    if(beg<end)
    {
        int p=part(beg,end);
        QuickSort(beg,p-1);
        QuickSort(p+1,end);
    }
}
int main()
{
    int n;
    cin>>n;
    for(int i=0; i<n; ++i)
        cin>>arr[i];
    QuickSort(0,n-1);
    for(int i=0;i<n;++i)
        cout<<arr[i]<<" ";
    cout<<endl;
    return 0;
}

　　

//poj 2104 K-th Number


#include <iostream>
using namespace std;
struct node 
{
    int index;
    int num;
}list[100000];
int part(int beg,int end)
{
    int low=beg,high=end;
    node pivot=list[beg];
    while(low < high)
    {
        while(low<high && list[high].num>=pivot.num)
            --high;
        list[low].index=list[high].index;
        list[low].num=list[high].num;
        while(low<high && list[low].num<=pivot.num)
            ++low;
        list[high].index=list[low].index;
        list[high].num=list[low].num;
    }
    list[low].index=pivot.index;    
    list[low].num=pivot.num;
    return low;
}
void QuickSort(int beg,int end)
{
    if(beg<end)
    {
        int p=part(beg,end);
        QuickSort(beg,p-1);
        QuickSort(p+1,end);
    }
}
int main()
{
    int n,m,t,i,j,k;
    scanf("%d%d",&n,&m);
    for(t=0;t<n;++t)
    {
        list[t].index=t+1;
        scanf("%d",&list[t].num);
    }
    QuickSort(0,n-1);
    while(m--)
    {
        scanf("%d%d%d",&i,&j,&k);
        for(t=0;t<n;++t)
        {
            if(list[t].index>=i&&list[t].index<=j)
                k--;
            if(k==0)
                break;
        }
        printf("%d\n",list[t].num);
    }    
    return 0;
}