LeetCode之“链表”：Remove Duplicates from Sorted List && Remove Duplicates from Sorted List II

　 1. Remove Duplicates from Sorted List

　　题目链接

　　题目要求：

　　Given a sorted linked list, delete all duplicates such that each element appear only once.

　　For example,
　　Given

1->1->2

, return

1->2

.
　　Given

1->1->2->3->3

, return

1->2->3

.

　　这道题不难。具体程序如下：

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* deleteDuplicates(ListNode* head) {
if(!head || !head->next)
return head;

int preVal = head->val;
ListNode *preNode = head;
ListNode *start = head->next;
while(start)
{
while(start && start->val == preNode->val)
{
ListNode *next = start->next;
preNode->next = next;
delete start;
start = next;
}

if(!start)
break;

preNode = start;
start = start->next;
}

return head;
}
};

　 2. Remove Duplicates from Sorted List II

　　题目链接

　　题目要求：

　　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

.

　　该题可以通过添加dummy节点以方便编程。具体程序如下：

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* deleteDuplicates(ListNode* head) {
if(!head || !head->next)
return head;

int preVal = head->val;
ListNode *dummy = new ListNode(0);
dummy->next = head;
ListNode *prepreNode = dummy, *preNode = head;
ListNode *start = head->next;
while(start)
{
bool flag = true;
while(start && start->val == preNode->val)
{
flag = false;
ListNode *next = start->next;
preNode->next = next;
delete start;
start = next;
}

if(flag)
{
prepreNode = preNode;
preNode = preNode->next;
}
else
{
prepreNode->next = preNode->next;
delete preNode;
preNode = prepreNode->next;
}

if(!preNode || !preNode->next)
break;
start = preNode->next;
}

head = dummy->next;
delete dummy;
dummy = nullptr;

return head;
}
};