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Remove Duplicates from Sorted List II

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Description

https://leetcode.com/problems/remove-duplicates-from-sorted-list-ii/description/

Solution

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/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
bool duplicate(struct ListNode* node) {
    if (node == NULL || node->next == NULL) return false;
    return node->val == node->next->val;
}


struct ListNode* deleteDuplicates(struct ListNode* head) {
    if (head == NULL || head->next == NULL) return head;
    
    struct ListNode* setinel_head = (struct ListNode* ) malloc(sizeof(struct ListNode));
    setinel_head->next = head;
    
    
    struct ListNode* pre = setinel_head;
    struct ListNode* current = head;
    while (current != NULL) {
        if (duplicate(current) == false) {
            pre = pre->next;
            current = pre->next;
        }else {
            struct ListNode* nextNode = current->next;
            while (nextNode != NULL && current->val == nextNode->val){
                nextNode = nextNode->next;
            }
            pre->next = nextNode;
            current = nextNode;
        }    
    } 
    return setinel_head->next;
}