83.删除排序链表中的重复元素

/**
 * 给定一个已排序的链表的头 head ， 删除所有重复的元素，使每个元素只出现一次 。返回 已排序的链表 。
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */

function ListNode(val, next) {
    this.val = (val === undefined ? 0 : val)
    this.next = (next === undefined ? null : next)
}

/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var deleteDuplicates = function (head) {
    let curr = head
    while(curr && curr.next) {
        if(curr.val === curr.next.val) {
            curr.next = curr.next.next
        } else {
            curr = curr.next
        }
    }
    return head
};

var deleteDuplicates = function (head) {
    if(!head || !head.next) {
        return null
    }
    head.next = deleteDuplicates(head)
    if(head.val === head.next.val) {
        head.next = head.next.next
    }
    return head
};