Return -1 in the case of overflow

#define max(a, b) (((a) >= (b)) ? (a) : (b))
#define min(a, b) (((a) >= (b)) ? (b) : (a))

int computeArea(int A, int B, int C, int D, int E, int F, int G, int H) {
        int tmp1, tmp2, tmp3, tmp4;
	long rec1Area, rec2Area, res = 0;

	rec1Area = (long)(C - A) * (D - B);
	if(rec1Area > INT_MAX) return -1;
	rec2Area = (long)(G - E) * (H - F);
	if(rec2Area > INT_MAX) return -1;
	res = rec1Area + rec2Area;
	if(((A <= G) && (E <= C)) && ((D >= F) && (H >= B))) {//overlapping
		tmp1 = max(A, E);
		tmp2 = min(C, G);
		tmp3 = min(D, H);
		tmp4 = max(B, F);
		res = res - (tmp2 - tmp1) * (tmp3 - tmp4);
		if(res > INT_MAX) return -1;
		return (int)res;
	}
	if(res > INT_MAX) return -1;
	return (int)res;
}

struct ListNode* swapPairs(struct ListNode* head) {
    struct ListNode *p1, *p2, *p3;
    if (!head) return head;
    if (!head->next) return head;
    p1 = head;
    p2 = head->next;
    p3 = p2->next;
    p2->next = p1;
    p1->next = swapPairs(p3);
    return p2;
}