leetcode 日经贴，Cpp code -Remove Duplicates from Sorted List II

/**
* 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;
ListNode *ch = NULL, *cp = NULL;
while (head) {
if (!head->next || head->val != head->next->val) {
if(!ch) {
ch = cp = head;
} else {
cp->next = head;
cp = head;
}
head = head->next;
} else {
int val = head->val;
while (head && head->val == val) {
head = head->next;
}
}
}
if(cp) {
cp->next = NULL;
}
return ch;
}
};