LeetCode --- 82. Remove Duplicates from Sorted List II

82. Remove Duplicates from Sorted List II

Difficulty: Medium

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

Example 1:

Input: 1->2->3->3->4->4->5
Output: 1->2->5

Example 2:

Input: 1->1->1->2->3
Output: 2->3

Solution

思路

1. 申请一个newHead指向head。
2. 遍历cur->next，如果和cur的值相同，cur向下移动，如果不相同，先判断pre和cur是否相邻，如果相邻pre=cur，如果不相邻，删除重复元素。
3. 最后判断是否一直为重复元素，如果一直是重复元素，则删除。

Language: C++

/**
 * 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) {
        ListNode* newHead = new ListNode(0);
        newHead->next = head;
        if (!head || !head->next) return head;
        ListNode* pre = newHead, *cur = newHead->next;
        while (cur->next){
            if (cur->next->val != cur->val){
                if (pre->next == cur)
                    pre = cur;
                else
                    pre->next = cur->next;
            }
            cur = cur->next;
        }
        if (pre->next != cur)
            pre->next = cur->next;
        return newHead->next;
    }
};