added 94. Remove Duplicates from Sorted List II

94. Remove Duplicates from Sorted List II/README.md

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+这道题没有太多可说的，属于基本题的扩展。
+
+可以先参考前面的 [12. Remove Duplicates from Sorted List](../12. Remove Duplicates from Sorted List).
+
+而这道题多出的一点把戏在于，要把重复的数据删的干干净净。我的策略很简单，将重复的数据做一个标记，`isDuplicate`, 然后再删掉重复元素的基础上，最后给剩下那个光棍补上一刀。
+
+虽然有点啰嗦，但是效率还过得去。

94. Remove Duplicates from Sorted List II/main.cpp

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+#include "solution.h"
+#include <iostream>
+
+using namespace std;
+
+ListNode *create_linkedlist(std::initializer_list<int> lst)
+{
+    auto iter = lst.begin();
+    ListNode *head = lst.size() ? new ListNode(*iter++) : NULL;
+    for (ListNode *cur=head; iter != lst.end(); cur=cur->next)
+        cur->next = new ListNode(*iter++);
+    return head;
+}
+
+int main()
+{
+    Solution s;
+    ListNode *head = s.deleteDuplicates(create_linkedlist({1,1,2,2,3,4}));
+    for (ListNode *cur=head; cur; cur=cur->next)
+        std::cout << cur->val << "->";
+    std::cout << "\b\b  " << std::endl;
+
+    return 0;
+}
+

94. Remove Duplicates from Sorted List II/solution.h

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+#include <cstddef> 
+
+struct ListNode {
+    int val;
+    ListNode *next;
+    ListNode(int x) : val(x), next(NULL) {}
+};
+
+class Solution {
+public:
+    ListNode *deleteDuplicates(ListNode *head) {
+        if (head == NULL) return head;
+        ListNode preHead(0);
+        preHead.next = head;
+        ListNode *pre = &preHead;
+        bool isDuplicate = false;
+        ListNode *p = head;
+        while (p->next)
+            if (p->val == p->next->val) {
+                ListNode *next = p->next->next;
+                delete p->next;
+                p->next = next;
+                isDuplicate = true;
+            } else if (isDuplicate) {
+                ListNode *next = p->next;
+                delete p;
+                p = next;
+                pre->next = p;
+                isDuplicate = false;
+            } else {
+                pre = p;
+                p = p->next;
+            }
+        if (isDuplicate) {
+            ListNode *next = p->next;
+            delete p;
+            pre->next = next;
+        }
+        return preHead.next;
+    }
+};