83 Remove Duplicates from Sorted List

给定一个排序链表，删除所有重复元素，使得每个元素只出现一次。

重复的情况下指向下一个指针

• 时间复杂度 O(1)，空间复杂度O(1）
• Runtime: 92 ms, faster than 64.01%
• Memory Usage: 40.4 MB, less than 70.73%

/**
 * Definition for singly-linked list.
 * 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 res = head
    while(head && head.next) {
        while(head.next && head.val === head.next.val) {
            head.next = head.next.next
        }
        head = head.next
    }
    return res
};