#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

/* max heap implementation */

/* compute child 0 or 1 */
#define Child(x, dir) (2*(x)+1+(dir))

/* float value at position pos down */
static void
floatDown(int n, int *a, int pos)
{
    int x;

    /* save original value once */
    x = a[pos];

    for(;;) {
        if(Child(pos, 1) < n && a[Child(pos, 1)] > a[Child(pos, 0)]) {
            /* maybe swap with Child(pos, 1) */
            if(a[Child(pos, 1)] > x) {
                a[pos] = a[Child(pos, 1)];
                pos = Child(pos, 1);
            } else {
                /* x is bigger than both kids */
                break;
            }
        } else if(Child(pos, 0) < n && a[Child(pos, 0)] > x) {
            /* swap with Child(pos, 0) */
            a[pos] = a[Child(pos, 0)];
            pos = Child(pos, 0);
        } else {
            /* done */
            break;
        }
    }

    a[pos] = x;
}

/* construct a heap bottom-up */
static void
heapify(int n, int *a)
{
    int i;

    for(i = n-1; i >= 0; i--) {
        floatDown(n, a, i);
    }
}

/* sort an array */
void
heapSort(int n, int *a)
{
    int i;
    int tmp;

    heapify(n, a);

    for(i = n-1; i > 0; i--) {
        /* swap max to a[i] */
        tmp = a[0];
        a[0] = a[i];
        a[i] = tmp;

        /* float new a[0] down */
        floatDown(i, a, 0);
    }
}

#define N (100)
#define MULTIPLIER (17)

int
main(int argc, char **argv)
{
    int a[N];
    int i;

    if(argc != 1) {
        fprintf(stderr, "Usage: %s\n", argv[0]);
        return 1;
    }

    for(i = 0; i < N; i++) { a[i] = (i*MULTIPLIER) % N; }

    for(i = 0; i < N; i++) { printf("%d ", a[i]); }
    putchar('\n');

    heapSort(N, a);

    for(i = 0; i < N; i++) { printf("%d ", a[i]); }
    putchar('\n');

    return 0;
}