poj 2388 堆排序

找中位数

#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;

#define father(i) (i>>1)
#define left(i) (i<<1)
#define right(i) (i<<1|1)
#define swap(a,b) {int t=a;a=b;b=t;}

int heap_size;
int a[10010];

void max_heapify(int i)
{
    int l=left(i);
    int r=right(i);
    int largest;
    if(l<=heap_size&&a[l]>a[i])
        largest=l;
    else
        largest=i;

    if(r<=heap_size&&a[r]>a[largest])
        largest=r;

    if(largest!=i){
        swap(a[i],a[largest]);
        max_heapify(largest);
    }
}

void build_max_heap()
{
    for(int i=heap_size/2;i>=1;i--)
        max_heapify(i);
}

void heap_sort()
{
    for(int i=heap_size;i>=2;i--){
        swap(a[1],a[i]);
        heap_size--;
        max_heapify(1);
    }
}

int main()
{
    int n;
    //freopen("in.txt","r",stdin);
    while(~scanf("%d",&n))
    {
        for(int i=1;i<=n;i++)
            scanf("%d",&a[i]);
        heap_size=n;

        build_max_heap();
        heap_sort();
        printf("%d\n",a[n/2+1]);
    }
    return 0;
}