83. 删除排序链表中的重复元素

/**
 * 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) {
  if(!head){
    return head;
  }
  let cur = head;
  while(cur.next){
    if(cur.val === cur.next.val){
      cur.next = cur.next.next;
    }else{
      cur = cur.next;
    }
  }
  return head;
};

/**
 * 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 cur = head;
  let pre = cur;
  let hash = new Map();
  while(cur){
    let val = cur.val;
    if(!hash.has(val)){
      hash.set(val, 1);
      pre = cur;
    }else{
      pre.next = cur.next;
    }
    cur = cur.next;
  }
  return head;
};