LeetCode＃19. Delete the penultimate node of the linked list

For this problem, we can first get the sum of the number of nodes in the linked list （ Here I use count To express ）, Then judge when the special situation （ Request to delete the first node ） And normal operation , Then carry out the corresponding steps .

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def removeNthFromEnd(self, head: ListNode, n: int) -> ListNode:
        count=0
        pre=head
        cur=head
        while pre != None:
            count+=1
            pre=pre.next # Get the length count
        if count-n==0:
            return head.next
        for i in range(count-n-1):
            cur=cur.next
        cur.next=cur.next.next
        return head