# 移除链表元素（203）

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
export const removeElements = (head, val) => {
	if (!head) return null;
	head.next = removeElements(head.next, val);
	return head.val === val ? head.next : head;
};

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
export const removeElements = (head, val) => {
	let sentinel = new ListNode();
	sentinel.next = head;
	let prev = sentinel,
		cur = head;
	while (cur) {
    // 如果cur.val===val，那么prev.next指向cur的下一个，prev的指针不变
    // 否则让prev的指针向前移动一步
    // 无论是否相等，cur都向后移动一步
		if (cur.val === val) {
			prev.next = cur.next;
		} else {
			prev.next = cur;
		}
		cur = cur.next;
	}
	return sentinel.next;
};