[LeetCode] 083: Remove Duplicates from Sorted List II

[Problem]

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.

[Solution]

/**
 * 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) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(head != NULL){
            ListNode *pre = head;
            ListNode *begin = head;
            ListNode *end = head->next;
   
            // find duplicates
            while(end != NULL){
                // found
                if(begin->val == end->val){
                    // find duplicates
                    while(end != NULL && begin->val == end->val){
                        end = end->next;
                    }
   
                    // head is one of the duplicates
                    if(pre->val == begin->val){
                        head = end;
                        pre = head;
                        begin = head;
                        if(head != NULL){
                            end = head->next;
                        }
                    }
                    // head is uniq
                    else{
                        // remove dunplicates
                        pre->next = end;
   
                        // reset pre, begin and end
                        begin = end;
                        if(end != NULL){
                            end = end->next;
                        }
                    }
                }
                // not found
                else{
                    pre = begin;
                    begin = end;
                    end = end->next;
                }
            }
        }
        return head;
    }
};

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