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【LeetCode】Remove Duplicates from Sorted List II

题目

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

For example,
Given 1->2->3->3->4->4->5, return 1->2->5.
Given 1->1->1->2->3, return 2->3.

解答

Remove Duplicates from Sorted List有点类似,只是这里要把出现重复的元素全部删除。其实道理还是一样,只是现在要把前驱指针指向上一个不重复的元素中,如果找到不重复元素,则把前驱指针知道该元素,否则删除此元素。代码如下:

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        if(head==null||head.next==null){
            return head;
        }
        ListNode fakeHead=new ListNode(-1);  //前驱指针
        fakeHead.next=head;
        ListNode pre=fakeHead;
        ListNode cur=head;
        while(cur!=null){
            //若头部重复
            while(cur.next!=null&&pre.next.val==cur.next.val){
                cur=cur.next;
            }
            
            if(pre.next==cur){
                pre=pre.next;  //头部无重复,移动pre
            }else{
                pre.next=cur.next;
            }
            cur=cur.next;
        }
        return fakeHead.next;
    }
}


//笨方法,超时
public class Solution {
    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){   //判断头部是否重复
                ListNode pre=cur.next;
                while(pre!=null&&pre.next!=null&&pre.val==pre.next.val){
                    pre.next=pre.next.next;
                }
                if(pre.next!=null){
                    cur.next=pre.next;   //当while从pre.next==null退出时,保留pre当前点
                }
            }else{
                ListNode temp=cur.next;
                while(temp!=null&&cur.val==temp.val){
                    temp=temp.next;
                }
                head=temp;
                cur=head;
            }
        }
        return head;
    }
}

---EOF---

【LeetCode】Remove Duplicates from Sorted List II