#define LeftChild(i) (2*(i)+1)

void PercDown(ElementType A[], int i, int N) {
    int child;
    ElementType 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(ElementType A[], int N) {
    int i;
    for (i=N/2; i>=0; i++) {
        PercDown(A, N);
    }
    for (i=N-1; i>0; i--) {
        swap(&A[0], &A[i]);
        PercDown(A, 0, i);
    }
}