HDU 1425 sort（堆排序/快排/最大堆/最小堆）

传送门

Description

给你n个整数，请按从大到小的顺序输出其中前m大的数。

Input

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。

Output

对每组测试数据按从大到小的顺序输出前m大的数。

Sample Input

5 3 
3 -35 92 213 -644

Sample Output

213 92 3

1、使用内建sort函数

#include<iostream>
#include<algorithm>
#include<cstdio>
using namespace std;
int ans[1000001];
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);
        printf("%d",ans[n - 1]);
        for(int i = n - 2;m > 1;m--,i--)
        {
            printf(" %d",ans[i]);
        } 
        printf("\n");
    }
    return 0;
} 

2、使用内建优先队列

#include<iostream>
#include<queue>
#include<cstdio>
using namespace std;

int main()
{
    int N,M;
    while (~scanf("%d%d",&N,&M))
    {
        priority_queue<int>que;
        bool first = true;
        int tmp;
        while (N--)
        {
            scanf("%d",&tmp);
            que.push(tmp);
        } 
        while (M--)
        {
            first?printf("%d",que.top()):printf(" %d",que.top());
            que.pop();
            first = false;
        }
        printf("\n");
    }
    return 0;
}

3、使用内部堆函数

#include <cstdio>
#include <algorithm>
using namespace std;

static int a[1000000];

int main()
{
    int i,n,m;
    while(EOF != scanf("%d %d",&n,&m))
    {
        for(i=0;i<n;i++)
            scanf("%d",&a[i]);
        make_heap(a,a+n);
        printf("%d",a[0]);
        for(i=1;i<m;i++)
        {
            pop_heap(a,a+n-i+1);
            printf(" %d",a[0]);
        }
        printf("\n");
    }
    return 0;
}

4、手写最大堆

#include<stdio.h>
#include<string.h>
const int maxn = 1000005;
int heap[maxn],sz = 0;

void push(int x)
{
    int i = sz++;
    while (i > 0)
    {
        int p = (i - 1)/2;
        if (heap[p] >= x)    break;
        heap[i] = heap[p];
        i = p;
    }
    heap[i] = x;
}

int pop()
{
    int ret = heap[0];
    int x = heap[--sz];
    int i = 0;
    while (i*2+1<sz)
    {
        int a = i*2+1,b = i*2+2;
        if (b < sz && heap[b]>heap[a])    a = b;
        if (heap[a] <= x)    break;
        heap[i] = heap[a];
        i = a;
    }
    heap[i] = x;
    return ret;
}

int main()
{
    int n,m,tmp;
    while (~scanf("%d%d",&n,&m))
    {
        sz = 0;
        memset(heap,0,sizeof(heap));
        for (int i = 0;i < n;i++)    scanf("%d",&tmp),push(tmp);
        for (int i = 1;i < m;i++)    printf("%d ",pop());
        printf("%d\n",pop());
    }
    return 0;
}　

5、手写堆排序（从大到小）

#include<bits/stdc++.h>
using namespace std;
#define LeftChild(i) (2*(i)+1)
const int maxn = 1000005;
int a[maxn]; 

void PercDown(int a[],int i,int N)
{
    int Child;
    int tmp;
    for (tmp = a[i];LeftChild(i) <N;i = Child)
    {
        Child = LeftChild(i);
        if (Child != N - 1 && a[Child+1] < a[Child])
            Child++;
        if (tmp > a[Child])
            a[i] = a[Child];
        else
            break;
    }
    a[i] = tmp;
}

void Heapsort(int a[],int N)
{
    int i;
    for (i = N/2;i >= 0;i--)
        PercDown(a,i,N);
    for (i = N-1;i > 0;i--)
    {
        swap(a[0],a[i]);
        PercDown(a,0,i);
    }
}

int main()
{
    int n,m;
    while (~scanf("%d%d",&n,&m))
    {
        for (int i = 0;i < n;i++)    scanf("%d",&a[i]);
        Heapsort(a,n);
        printf("%d",a[0]);
        for (int i = 1;i < m;i++)    printf(" %d",a[i]);
        printf("\n");
    }
    return 0;
}

6、手写堆排序（从小到大）

#include<cstdio>
#include<algorithm>
using namespace std;
#define LeftChild(i) (2*(i)+1)
const int maxn = 1000005;
int a[maxn]; 

void PercDown(int a[],int i,int N)
{
    int Child;
    int tmp;
    for (tmp = a[i];LeftChild(i) <N;i = Child)
    {
        Child = LeftChild(i);
        if (Child != N - 1 && a[Child+1] > a[Child])
            Child++;
        if (tmp < a[Child])
            a[i] = a[Child];
        else
            break;
    }
    a[i] = tmp;
}

void Heapsort(int a[],int N)
{
    int i;
    for (i = N/2;i >= 0;i--)
        PercDown(a,i,N);
    for (i = N-1;i > 0;i--)
    {
        swap(a[0],a[i]);
        PercDown(a,0,i);
    }
}

int main()
{
    int n,m;
    while (~scanf("%d%d",&n,&m))
    {
        for (int i = 0;i < n;i++)    scanf("%d",&a[i]);
        Heapsort(a,n);
        printf("%d",a[n-1]);
        for (int i = n-2;i > n-1 - m;i--)    printf(" %d",a[i]);
        printf("\n");
    }
    return 0;
}

7、手写快速排序（从大到小）

#include<bits/stdc++.h>
using namespace std;
#define Cutoff (3)
const int maxn = 1000005;
int a[maxn];

void InsertionSort(int a[],int N)
{
    int i,j,tmp;
    for (i = N - 2;i >= 0;i--)
    {
        tmp = a[i];
        for (j = i;j < N - 1 && a[j + 1] > tmp;j++)
            a[j] = a[j + 1];
        a[j] = tmp;
    }
}

int median3(int a[],int left,int right)
{
    int center = (left + right) / 2;
    if (a[left] < a[center])
        swap(a[left],a[center]);
    if (a[left] < a[right])
        swap(a[left],a[right]);
    if (a[center] < a[right])
        swap(a[center],a[right]);
    swap(a[center],a[left + 1]);
    return a[left + 1];
}

void qsort(int a[],int left,int right)
{
    int i,j,pivot;
    if (left + Cutoff <= right)
    {
        pivot = median3(a,left,right);
        i = left + 1;j = right;
        for (;;)
        {
            while (a[++i] > pivot){}
            while (a[--j] < pivot){}
            if (i < j)    swap(a[i],a[j]);
            else    break;
        }
        swap(a[j],a[left + 1]);
        qsort(a,left,j - 1);
        qsort(a,j + 1,right);
    }
    else    InsertionSort(a + left,right - left + 1);
}

int main()
{
    int n,m;
    while (~scanf("%d%d",&n,&m))
    {
        for (int i = 0;i < n;i++)    scanf("%d",&a[i]);
        qsort(a,0,n - 1);
        printf("%d",a[0]);
        for (int i = 1;i < m;i++)    printf(" %d",a[i]);
        printf("\n");
    }
    return 0;
} 

8、手写快速排序（从小到大）

#include<bits/stdc++.h>
using namespace std;
const int Cutoff = 10;
const int maxn = 1000005;
int a[maxn];
void InsertionSort(int a[],int N)
{
    int i,j,tmp;
    for (i = 1;i < N;i++)
    {
        tmp = a[i];
        for (j = i;j > 0 && a[j - 1] > tmp;j--)
            a[j] = a[j - 1];
        a[j] = tmp;
    }
}
int median3(int a[],int left,int right)
{
    int center = (left + right) / 2;
    if (a[left] > a[center])
        swap(a[left],a[center]);
    if (a[left] > a[right])
        swap(a[left],a[right]);
    if (a[center] > a[right])
        swap(a[center],a[right]);
    swap(a[center],a[right-1]);
    return a[right-1];
}
void qsort(int a[],int left,int right)
{
    int i,j,pivot;
    if (left + Cutoff <= right)
    {
        pivot = median3(a,left,right);
        i = left;j = right-1;
        for (;;)
        {
            while (a[++i] < pivot){}
            while (a[--j] > pivot){}
            if (i < j)    swap(a[i],a[j]);
            else    break;
        }
        swap(a[i],a[right-1]);
        qsort(a,left,i - 1);
        qsort(a,i + 1,right);
    }
    else    InsertionSort(a + left,right - left + 1);
}
int main()
{
    int n,m;
    while (~scanf("%d%d",&n,&m))
    {
        for (int i = 0;i < n;i++)    scanf("%d",&a[i]);
        qsort(a,0,n - 1);
        printf("%d",a[n - 1]);
        for (int i = n - 2;i > n - m - 1;i--)    printf(" %d",a[i]);
        printf("\n");
    }
    return 0;
}