题解 | #删除有序链表中重复的元素-I#

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    public ListNode deleteDuplicates2 (ListNode head) {
        // write code here
        if (head == null || head.next == null) {
            return head;
        }
        Stack<ListNode> stack = new Stack<>();
        ListNode cur = head;
        while (cur != null) {
            if (stack.isEmpty() || stack.peek().val != cur.val) {
                stack.push(cur);
            }
            cur = cur.next;
        }
        ListNode newHead = stack.pop();
        newHead.next = null;
        while (!stack.isEmpty()) {
            cur = stack.pop();
            cur.next = newHead;
            newHead = cur;
        }
        return newHead;
    }

    public ListNode deleteDuplicates (ListNode head) {
        if (head == null || head.next == null) {
            return head;
        }
        ListNode cur = head;
        while (cur != null && cur.next != null) {
            if (cur.val == cur.next.val) {
                cur.next = cur.next.next;
            } else {
                cur = cur.next;
            }
        }
        return head;
    }






}