Remove Duplicates from Sorted List

Remove Duplicates from Sorted List

Given a sorted linked list, delete all duplicates such that each element appear only once.

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

/**
 * 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) return NULL;
        ListNode *fast = head->next, *slow = head;
        int lastVal = head->val;
        
        while (fast) {
            if (fast->val != lastVal) {
                slow->next->val = fast->val;
                slow = slow->next;
            }
            lastVal = fast->val;
            fast = fast->next;
        }
        slow->next = NULL;
        
        return head;
    }
};