//recursive approach
ListNode *swapPairs2(ListNode *head) {
if (NULL == head || NULL == head->next) return head;
ListNode *p = swapPairs2(head->next->next);
head->next->next = head;
head = head->next;
head->next->next = p;
return head;
}
int main() {
int i, n;
struct ListNode *head = NULL, *tmphead = NULL, *head1, *head2;
for(i = 15 ; i >= 1 ; i--) {
head = insert(head, i);
tmphead = insert(tmphead, i);
}
head1 = swapPairs1(head);
printf("First function: \n");
while(head1) {
printf("%d-->", head1->val);
head1 = head1->next;
}
printf("\n");
printf("Second function: \n");
head2 = swapPairs2(tmphead);
while(head2) {
printf("%d-->", head2->val);
head2 = head2->next;
}
printf("\n");
return 0;
}
ListNode *swapPairs(ListNode* head) {
//return swapPairs1(head);
return swapPairs2(head);
}
/*
* Here we have two ways to solve this problem:
* 1) keep the list's nodes no change. only swap the data in the list node.
* 2) swap the list node physically.
*/
ListNode *swapPairs(ListNode *head) {
if(random()%2){
return swapPairs1(head);
}
return swapPairs2(head);
}
