POJ-2388 who's in the middle

此题仅为堆排序的练习题——其实不用堆直接QSORT也可以——为最短路径做准备 :)

/*
 * POJ-2388 who's in the middle
 * mike-w
 * 2011-08-16
 * PS: 这也许本不是一道堆排序题，不过我用此题练习一下堆排序 ;)
 */
#include<stdio.h>
#define MAX_SIZE 10101

long heap[MAX_SIZE];	/* heap[0] indicates the number of totla elements */
long N;

long swap(long *t1,long *t2)
{
	long t3=*t1;
	*t1=*t2;
	*t2=t3;
	return 0;
}

int insert(long e)
{
	long n=++heap[0];
	heap[n]=e;
	while(heap[n]>heap[n/2]&&n>1)
		swap(heap+n,heap+n/2),n/=2;
	return 0;
}

long pop(void)
{
	long ret=heap[1];
	swap(heap+1,heap+*heap);
	*heap-=1;
	long n=1,t;
	while( (t=n<<1)<=*heap)
			if(t+1<=*heap && heap[t+1]>heap[t] && heap[n]<heap[t+1])
				swap(heap+n,heap+t+1),n=t+1;
			else if(heap[n]<heap[t])
				swap(heap+n,heap+t),n=t;
			else
				break;
	return ret;
}

int main(void)
{
#ifndef ONLINE_JUDGE
	freopen("2388.in","r",stdin);
#endif
	scanf("%ld",&N);
	long i,t1;

	for(i=0;i<N;i++)
	{
		scanf("%ld",&t1);
		insert(t1);
	}

	for(i=0;i<N/2;i++)
		pop();
	printf("%ld\n",pop());
	
	return 0;
}