多项式问题

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

typedef struct _node_ {
    int coef;
    int exp;
    struct _node_ *next;
}linknode_t, *linklist;

linklist linklist_init();
int linklist_insert(linklist h, int coef, int exp);
int linklist_show(linklist h);
int linklist_union(linklist h1, linklist h2);

int main()
{
    linklist h1 = NULL;
    linklist h2 = NULL;
    int i ,j;
    int a[][2] = {{5, 0}, {2, 1}, {9, 4}, {3, 16}, {8, 8}, {-30, 27}};
    int b[][2] = {{23, 16}, {6, 1}, {-8, 8}, {11, 11}, {25, 25}, {27, 27}};

    h1 = linklist_init();
    h2 = linklist_init();

    for (i = 0; i < sizeof(a) / sizeof(a[0]); i++)
        linklist_insert(h1, a[i][0], a[i][1]);
    for (j = 0; j < sizeof(b) / sizeof(b[0]); j++)
        linklist_insert(h2, b[j][0], b[j][1]);

    linklist_show(h1);
    putchar('\n');
    linklist_show(h2);

    puts("");
    linklist_union(h1, h2);
    linklist_show(h1);

    return 0;
}

linklist linklist_init()
{
    linklist h = NULL;

    h = (linklist)malloc(sizeof(linknode_t));

    if (NULL == h) {
        printf("fail to malloc!\n");
        return NULL;
    }

    h->next = NULL;

    return h;
}

int linklist_insert(linklist h, int coef, int exp)
{
    linklist p = h;
    linklist new = NULL;

    while (p->next && p->next->exp < exp)
        p = p->next;

    new = (linklist)malloc(sizeof(linknode_t));

    new->coef = coef;
    new->exp = exp;
    new->next = p->next;
    p->next = new;

    return 0;
}

int linklist_show(linklist h)
{
    linklist p = h->next;

    while (p) {
        printf("(%d,%d)\n", p->coef, p->exp);
        p = p->next;
    }

    return 0;
}

int linklist_union(linklist h1, linklist h2)
{
    linklist p = h1->next, q = h2->next, r = h1, s;
    h1->next = NULL;

    while (p && q) {
        if (p->exp < q->exp) {
            r->next = p;
            p = p->next;
            r = r->next;
            r->next = NULL;
        } else if (p->exp == q->exp) {
            p->coef += q->coef;
            if (0 == p->coef) {
                printf("==0\n");
                s = p;
                p = p->next;
                free(s);
                s = NULL;
            } else {
                r->next = p;
                p = p->next;
                r = r->next;
                r->next = NULL;
            }
            s = q;
            q = q->next;
            free(s);
            s = NULL;
        } else {
            r->next = q;
            q = q->next;
            r = r->next;
            r->next = NULL;
        }
    }

    if (p)
        r->next = p;
    else
        r->next = q;

    return 0;
}