LeetCode/83. Remove Duplicates from Sorted List.md

# [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;   
    }
};
```