LeetCode-M-Remove Duplicates from Sorted List II

題意

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

For example,
Given 1->2->3->3->4->4->5, return 1->2->5.
Given 1->1->1->2->3, return 2->3.

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解法

實現

/**
 * 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 || head->next == NULL) return head;
        ListNode* pre = head;
        ListNode* cur = head->next;
        ListNode* next = NULL;
        while(cur != NULL){
            if(pre->val != cur->val){
                if(next == NULL){
                    head = pre;
                    next = pre;
                }else{
                    next->next = pre;
                    next = pre;
                }
                pre = cur;
                cur = cur->next;
            }else{
                while(cur != NULL && cur->val == pre->val) cur = cur->next;
                if(cur == NULL && next == NULL) return NULL;
                else if(cur == NULL && next != NULL){
                    next->next = NULL;
                    return head;
                }else if(cur != NULL && next == NULL){
                    pre = cur;
                    cur = cur->next;
                    if(cur == NULL) return pre;
                }else{
                    next->next = cur;
                    pre = cur;
                    cur = cur->next;
                }
            }
        }
        return head;
    }
};