83. Remove Duplicates from Sorted L

Given the head of a sorted linked list, delete all duplicates such that each element appears only once. Return the linked list sorted as well.

Example 1:

Input: head = [1,1,2]
Output: [1,2]

Example 2:

Input: head = [1,1,2,3,3]
Output: [1,2,3]

Constraints:

• The number of nodes in the list is in the range [0, 300].
• -100 <= Node.val <= 100
• The list is guaranteed to be sorted in ascending order.

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        if(!head)return nullptr;
        ListNode*dummyHead=head;
        while(dummyHead->next!=NULL){
            if(dummyHead->val==dummyHead->next->val){
                dummyHead->next=dummyHead->next->next;
            }else{
                dummyHead=dummyHead->next;
            }
        }
        return head;
    }
};

注意：

        1.需要先判断链表是否为空

        2.因为需要直接在链表上进行删除操作，所以用dummyHead直接=head，之所以没有用Head直接操作，是为了return的时候方便找到最开始的Head位置。