一天一大 leet(移除重复节点)难度:简单 DAY-26

 输入：[1, 2, 3, 3, 2, 1]
 输出：[1, 2, 3]

 输入：[1, 1, 1, 1, 2]
 输出：[1, 2]

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var removeDuplicateNodes = function(head) {
  if (head == null) return head;
  const map = new Map();
  map.set(head.val, true);
  let node = head.next;
  let prev = head;
  while (node) {
    if (map.has(node.val)) {
      prev.next = node.next;
    } else {
      map.set(node.val, true);
      prev = prev.next;
    }
    node = node.next;
  }
  return head;
};

const removeDuplicateNodes = (head) => {
   let ob = head;
    while (ob != null) {
        let oc = ob;
        while (oc.next != null) {
            if (oc.next.val == ob.val) {
                oc.next = oc.next.next;
            } else {
                oc = oc.next;
            }
        }
        ob = ob.next;
    }
    return head;
};