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) {}
 * };
 */
class Solution {
public:
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        if(head == NULL)
            return NULL;
       // ListNode* list = head;
       // L//istNode* fast = head, *slow = head;
        ListNode* dummy = new ListNode(0);
        dummy->next = head;
        ListNode* fast = dummy;
        ListNode* slow = dummy;
        for(int i = 1; i <= n + 1; i++)
            fast = fast->next;
        
        while(fast != nullptr) {
            fast = fast->next;
            slow = slow->next;
        }
        slow->next = slow->next->next;
        return dummy->next;
    }
};