【朱迪的LeetCode刷题笔记】82. Remove Duplicates from Sorted List II #Medium #C

Judie

82. Remove Duplicates from Sorted List II #Medium

Given the head of a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list. Return the linked list sorted as well.

 
Example 1:

Input: head = [1,2,3,3,4,4,5]
Output: [1,2,5]


Example 2:

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

C

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */


struct ListNode* deleteDuplicates(struct ListNode* head) {
    struct ListNode *before = NULL;
    struct ListNode *current = head;
    if (head == NULL) {
        return NULL;
    } 
    struct ListNode *next = head->next;
    while (next) {
        if (current->val == next->val) {
            while (next && current->val == next->val) {
                current = current->next;
                next = next->next;
            }
            if (next == NULL) {
                if (before == NULL) {
                    return NULL;
                }
                before->next = NULL;
                return head;
            }
            current = current->next;
            next = next->next;
            if (before == NULL) {
                head = current;
            } else {
                before->next = current;
            }
        } else {
            before = current;
            current = current->next;
            next = next->next;
        }     
    }
    return head;
}

不愧是medium 想了三天qwq