poj2388Who's in the Middle【堆排序】

5
2
4
1
3
5

3

#include<cstdio>
#include<cstdlib>
#include<cstring>
using namespace std;
int A[10010];
int size;
void swap(int *a,int *b){
int t;
t=*a;
*a=*b;
*b=t;
}
void HeapAdjust(int i,int num){
int lson=i<<1;
int rson=(i<<1)+1;
int max=i;
if(i<=size/2){
if(lson<=num&&A[lson]>A[max]){
max=lson;
}
if(rson<=num&&A[rson]>A[max]){
max=rson;
}
if(max!=i){
swap(&A[i],&A[max]);
HeapAdjust(max,num);
}
}

}
void BuildHeap(){
for(int i=size>>1;i>=1;--i){
HeapAdjust(i,size);
}
}
void Heapsort(){
BuildHeap();
for(int i=size;i>=1;--i){
swap(&A[1],&A[i]);
HeapAdjust(1,i-1);
}
}
int main()
{
int i;
while(scanf("%d",&size)!=EOF){
for(i=1;i<=size;++i){
scanf("%d",&A[i]);
}
Heapsort();
printf("%d\n",A[size/2+1]);
}
return 0;
}