LC 0019 [M] Remove Nth Node From End of List - ALawliet/algorithms GitHub Wiki

https://www.youtube.com/watch?v=XVuQxVej6y8&ab_channel=NeetCode

# 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: Optional[ListNode], n: int) -> Optional[ListNode]:
        dum = ListNode(-1, head)
        left = dum # start at -1
        right = head
        
        # increment right n times
        while n > 0 and right:
            right = right.next
            n -= 1
            
        # increment both left and right until right is null
        while right:
            right = right.next
            left = left.next
            
        # delete by skipping over one
        left.next = left.next.next
        # l    n
        # 1 -> 2 -> 3
        return dum.next