poj 2388(スタックソート)

#include <iostream>
using namespace std;

#define swap(a, b) {int t = a; a = b; b = t;}
int A[10001], size;

int parent(int i) {
    return i/2;
}

int left(int i) {
    return i*2;
}

int right(int i) {
    return i*2+1;
}

void max_heapify(int i)
{
    int l, r, largest;
    l = left(i);
    r = right(i);
    if(l <= size && A[l] > A[i]) {
        largest = l;
    }
    else {
        largest = i;
    }
    if(r <= size && A[r] > A[largest]) {
        largest = r;
    }
    if(i != largest) {
        swap(A[i], A[largest]);
        max_heapify(largest);
    }
}

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

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