* function ListNode(x){
 *   this.val = x;
 *   this.next = null;
 * }
 */

/**
  * 
  * @param head ListNode类 
  * @return ListNode类
  */
function deleteDuplicates( head ) {
    // write code here
    if(!head || !head.next)    return head
    let fast = head.next,slow = head
    while(fast){
        if(fast.val == slow.val){
            slow.next = fast.next
            fast = fast.next
        }else{
            slow = slow.next
            fast = fast.next
        }
    }
    return head
}
module.exports = {
    deleteDuplicates : deleteDuplicates
};

alt