Create 83. Remove Duplicates from Sorted List.md

83. Remove Duplicates from Sorted List.md

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+# [83. Remove Duplicates from Sorted List](https://leetcode.com/problems/remove-duplicates-from-sorted-list/description/)
+# 思路
+去除链表中的重复元素。
+设置两个相邻的指针pre和p，pre代表已处理部分的最后一个节点，p代表待处理节点，比较pre和p的值来决定是否删除p；
+# C++
+```
+/**
+ * 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 == NULL) return head;
+        ListNode *pre = head, *p = head -> next, *dup; // dup是待删除的重复节点
+        while(p){
+            while(p !=NULL && p -> val == pre -> val){ // 若p的值等于pre的值
+                pre -> next = p -> next; // 指针跳过p
+                dup = p; 
+                dup -> next = NULL; 
+                delete dup;
+                p = pre -> next; // p指针后移
+            }
+            pre = p; // pre后移
+            if(p) p = p -> next;
+        }
+        return head;   
+    }
+};
+```