19. Remove Nth Node From End of List

/**
 * 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:
    int countnodes(ListNode* head){
        int count=0;
        while(head!=NULL){
            count++;
            head=head->next;
        }
        return count;
    }
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        if(head->next==NULL && n==1) return NULL;
        
        
        int count = countnodes(head);
        int num= count- n;
        
        if(num==0) {
            ListNode* temp= head;
            head= head->next;
            delete(temp);
            return head;
        }
        
        // ListNode* curr= head;
        ListNode* curr= head->next;
        ListNode* prev= head;
        for(int i=1; i<num; i++){
            curr= curr->next;
            prev= prev->next;
        }
        prev->next= curr->next;
        delete(curr);
        return head;
    }
};