0019_Remove_Nth_Node_From_End_of_List.cpp

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */

#pragma GCC optimize("Ofast","inline","ffast-math","unroll-loops","no-stack-protector")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native","f16c")
class Solution {
public:
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
        ListNode* dummy = new ListNode(0, head);
        ListNode* fast = dummy;
        ListNode* slow = dummy;
        while (n--) {
            fast = fast->next;
        }
        while (fast->next) {
            slow = slow->next;
            fast = fast->next;
        }
        slow->next = slow->next->next;
        return dummy->next;
    }
};