RemoveNthNode_TwoPointers.cpp

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        //Handle situation that list is null or only contain one element
        if(!head || !(head->next))
            return nullptr;
        
        ListNode *fast = head, *slow =head;
        int count = 0;
        
        while(fast->next != nullptr)
        {
            fast = fast->next;
            count ++;
            if(count> n)
            {
                slow = slow->next;
            }
        }
        //Handles situation that we need to delete first node. e.g. [1,2] 2
        if(count + 1 == n)
        {
            head = head-> next;
            delete slow;
            return head;
        }
        ListNode *temp = slow->next;
        if(temp == nullptr)
            return nullptr;
        slow->next = temp->next; 
        delete temp;
        return head;
    }
};