题解 | 删除有序链表中重复的元素-II

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param head ListNode类
     * @return ListNode类
     */
    public ListNode deleteDuplicates (ListNode head) {
        if (head == null || head.next == null) {
            return head;
        }

        ListNode result = head;
        ListNode temp = null;
        ListNode slow = head;
        ListNode fast = head.next;

        boolean hasSame = false;
        while (fast != null) {
            if (fast.val != slow.val) {
                if (temp == null) {
                    // 处理开头就有重复数据的情况
                    if (!hasSame) {
                        result = slow;
                        temp = result;
                    }
                } else {
                    if (!hasSame) {
                        temp.next = slow;
                        temp = temp.next;
                    } else {
                        slow = fast;
                        fast = fast.next;
                        hasSame = false;
                        continue;
                    }
                }
                slow = fast;
                fast = fast.next;
                hasSame = false;
            } else {
                hasSame = true;
                if (fast.next == null) {
                    break;
                } else {
                    fast = fast.next;
                }
            }
        }

        // 处理结尾是重复数据的情况
        if (hasSame) {
            if (temp == null) {
                return temp;
            }
            temp.next = null;
        } else {
            if(temp == null) {
                return slow;
            } else {
                temp.next = slow;
            }
        }
        return result;
    }
}