LeetCode234.c

/*************************************************************************
    > File Name: LeetCode234.c
    > Author: ws
    > Mail: ws1519704327@126.com 
    > Created Time: 2020年02月26日 星期三 17时28分45秒
 ************************************************************************/


int get_length(struct ListNode *head) {
	int n = 0;
	while (head) n += 1, head = head->next;
	return n;
}

struct ListNode *get_node(struct ListNode *head, int ind) {
	while (ind--) head = head->next;
	return head;
}

struct ListNode *reverse(struct ListNode *head) {
	struct ListNode ret, *p = head, *q;
	ret.next = NULL;
	while (p) {
		q = p->next;
		p->next = ret.next;
		ret.next = p;
		p = q;
	}
	return ret.next;
}

bool isPalindrome(struct ListNode *head) {
	int len = get_length(head);
	struct ListNode *p = head, *q = reverse(get_node(head, (len + 1) / 2));
	while (q) {
		if (p->val - q->val) return false;
		p = p->next;
		q = q->next;
	}
	return true;
}