19. delete the penultimate node of the linked list

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subject ：19. Delete the last of the linked list N Nodes
describe ： I'll give you a list , Delete the last of the linked list n Nodes , And return the head node of the list .

Their thinking

1、 You can use arrays to store linked list nodes ;
2、 With a double pointer , See the code ;

Source code ##

class Solution {
    
public:
    ListNode* removeNthFromEnd(ListNode* head, int n) {
    
        ListNode *p = head;
        ListNode *slow = head;
        ListNode *fast = head;
        for (int i = 0; i < n; ++i) {
    
            fast = fast->next;
        }
        if (!fast) return slow->next;
        while (fast->next) {
    
            slow = slow->next;
            fast = fast->next;
        }
        slow->next = slow->next->next;
        return p;
    }
};