HDU1425 <sort 快排>

给你n个整数，请按从大到小的顺序输出其中前m大的数。

每组测试数据有两行，第一行有两个数n,m(0<n,m<1000000)，第二行包含n个各不相同，且都处于区间[-500000,500000]的整数。<快排>

//sort也可以过//936Ms
#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
const int maxn=1000005;
int ans[maxn];
bool cmp(int a,int b)
{
    return a>b;
}
int main ()
{
    int n,m;
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        for(int i=0;i<n;i++)
            scanf("%d",&ans[i]);
        sort(ans, ans+n, cmp);
        for(int i=0;i<m-1;i++)
            printf("%d ",ans[i]);
        printf("%d\n",ans[m-1]);
    }
    return 0;
}

//快排1//873Ms
#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
const int maxn=1000005;
int ans[maxn];
void quickSort(int l,int r)
{
    if(l>=r)
        return ;
    int i,j;
    for(j=i=l+1;i<=r;i++)
        if(ans[i]>ans[l])
            swap(ans[i],ans[j++]);
    swap(ans[l],ans[--j]);
    quickSort(l, j-1);
    quickSort(j+1, r);
}
/*bool cmp(int a,int b)
{
    return a>b;
}*/
int main ()
{
    int n,m;
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        for(int i=0;i<n;i++)
            scanf("%d",&ans[i]);
        //sort(ans, ans+n, cmp);
        quickSort(0, n-1);
        for(int i=0;i<m-1;i++)
            printf("%d ",ans[i]);
        printf("%d\n",ans[m-1]);
    }
    return 0;
}

//快排2//982ms
#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
const int maxn=1000005;
int ans[maxn];
void quickSort(int l,int r)
{
    if(l>=r)
        return ;
    int left=l,right=r,temp=ans[left];
    while(left<right)
    {
        while(left<right&&ans[right]<=temp)
            right--;
        ans[left]=ans[right];
        while(left<right&&ans[left]>=temp)
            left++;
        ans[right]=ans[left];
    }
    ans[left]=temp;
    quickSort(l,left-1);
    quickSort(left+1, r);
}
/*bool cmp(int a,int b)
{
    return a>b;
}*/
int main ()
{
    int n,m;
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        for(int i=0;i<n;i++)
            scanf("%d",&ans[i]);
        //sort(ans, ans+n, cmp);
        quickSort(0, n-1);
        for(int i=0;i<m-1;i++)
            printf("%d ",ans[i]);
        printf("%d\n",ans[m-1]);
    }
    return 0;
}

//快排3//624Ms
#include <iostream>
#include <string.h>
#include <cstdio>
#include<algorithm>
using namespace std;
const int N=1000005;
int num[N];
int partition(int low,int high){
    int i=low,j=high,key=num[low];
    while(i<j){
        while(i<j&&num[j]>key)
            --j;
        swap(num[i],num[j]);
        //int t=num[i]; num[i]=num[j];num[j]=t;
        while(i<j&&num[i]<key)
            ++i;
        swap(num[i],num[j]);
        //t=num[i]; num[i]=num[j];num[j]=t;
        }
    return i;
}
void quick_sort(int low,int high){
    if(low<high){
        int x=partition(low,high);
        quick_sort(low,x-1);
        quick_sort(x+1,high);
    }
}
int main(){
    //freopen("11.txt","r",stdin);
    int n,m;
    while(~scanf("%d%d",&n,&m)){
        for(int i=0;i<n;++i)
            scanf("%d",&num[i]);
        quick_sort(0,n-1);
        for(int i=n-1;i>n-m;--i)
            printf("%d ",num[i]);
        printf("%d",num[n-m]);
        printf("\n");
    }
    return 0;
}