solve.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>
struct ListNode {
	int val;
	struct ListNode *next;
};
int getLength(struct ListNode *head)
{
	int len = 0;
	struct ListNode *p = head;
	while (p) {
		++len;
		p = p->next;
	}
	return len;
}
void print(struct ListNode *head)
{
	if (head == NULL) {
		printf("NULL\n");
		return;
	}
	struct ListNode *p = head;
	while (p) {
		printf("%d ", p->val);
		p = p->next;
	}
	printf("\n");
}
struct ListNode * mk_list(struct ListNode **ha, int a[], int n)
{
	struct ListNode *p = malloc(sizeof(*p));
	p->val = a[0];
	p->next = NULL;
	*ha = p;
	for (int i = 1; i < n; ++i) {
		struct ListNode *q = malloc(sizeof(*q));
		q->val = a[i];
		q->next = NULL;
		p->next = q;
		p = q;
	}
	return p;
}
void free_list(struct ListNode *head)
{
	struct ListNode *p = head;
	while (p) {
		struct ListNode *q = p->next;
		free(p);
		p = q;
	}
}
struct ListNode* deleteDuplicates(struct ListNode *head)
{
	struct ListNode *p = head, *pre = NULL;
	while (p) {
		struct ListNode *q = p->next; // q is the next node of p
		bool isDup = false;
		while (q && q->val == p->val) {
			isDup = true;
			// delete q
			p->next = p->next->next;
			free(q);
			// update q
			q = p->next;
		}
		if (isDup) {
			if (p == head) {
				head = p->next;
				free(p);
				p = head;
			} else {
				pre->next = pre->next->next;
				free(p);
				p = q;
			}
		} else {
			pre = p;
			p = p->next;;
		}
	}
	return head;
}
int main(int argc, char **argv)
{
	struct ListNode *head = NULL;
	int a[] = {1,1,1,2,2,3,4,4,5,6,6};
	mk_list(&head, a, 11);
	print(head);
	head = deleteDuplicates(head);
	print(head);
	return 0;
}