面试题 02.01. Remove Duplicate Node LCCI

Problem

Write code to remove duplicates from an unsorted linked list.

Example1

Input: [1, 2, 3, 3, 2, 1]
Output: [1, 2, 3]

Example2

Input: [1, 2, 3, 3, 2, 1]
Output: [1, 2, 3]

Solution

用一个set辅助记录出现过的数字。
遍历链表的过程中，记录当前节点（cur）及其前驱节点（prev）。

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* removeDuplicateNodes(ListNode* head) {
        if(!head || !head->next)
            return head;
        unordered_set<int> h_set;

        ListNode *cur = head;
        ListNode *prev = NULL;
        while(cur)
        {
            if(h_set.find(cur->val) == h_set.end())
            {
                h_set.insert(cur->val);
                prev = cur;
                cur = cur->next;
                
            }
            else
            {
                prev->next = cur->next;
                delete cur;
                cur = prev->next;
            }

        }

        return head;

    }
};