Remove Duplicates from Sorted List II

Desicription

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.

Solution

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/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
trueListNode* deleteDuplicates(ListNode* head) {
ListNode* fake_head = new ListNode(0);
fake_head->next = head;
ListNode* pre = fake_head;
ListNode* now = head;
while(now){
while(now->next && now->val == now->next->val)
now = now->next;
if(pre->next == now)
pre = pre->next;
else
pre->next = now->next;
now = now->next;
}
return fake_head->next;
}
};