19. Remove Nth Node From End of List
MediumLeetCodeGiven the head of a linked list, remove the nth node from the end of the list and return its head.
Example 1
Input: head = [1,2,3,4,5], n = 2
Output: [1,2,3,5]
Example 2
Input: head = [1], n = 1
Output: []
Example 3
Input: head = [1,2], n = 1
Output: [1]
Constraints:
- The number of nodes in the list is sz
- 1 <= sz <= 30
- 0 <= Node.val <= 100
- 1 <= n <= sz
How to solve the problem
Code
Python
# 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]:
# Fast and slow pointer
dummyhead = ListNode(0, head)
fast = dummyhead
slow = dummyhead
for _ in range(n): # Let fast pointer move n step first
fast = fast.next
while(fast.next != None): # Move slow and fast pointer simultaneously
fast = fast.next
slow = slow.next
slow.next = slow.next.next # Let node(n-1) point to node(n+1)
return dummyhead.next
Complexity
- Time complexity: O(n)
- Space complexity: O(1)
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