[Solved] Given the head of a linked list, remove the nth node from the end of the list and return its head.

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Table of Contents

Question

Given the head of a linked list, remove the nth node from the end of the list and return its head.

Example 1:

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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

Follow up: Could you do this in one pass?

Python Solution

# 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:
        p1 = head
        p2 = head
        
        for _ in range(n):
            if p2:
                p2 = p2.next
            else:
                break
        
        if p2==None:
            return head.next
        
        while p2.next:
            p1 = p1.next
            p2 = p2.next
        
        p1.next = p1.next.next
        return head

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