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19. Remove Nth Node From End of List

Medium

Given 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

Follow up: Could you do this in one pass?

Solution

import { ListNode } from '../../com_github_leetcode/listnode'

let localN: number

function removeNthFromEnd(head: ListNode | null, n: number): ListNode | null {
    localN = n
    const dummy = new ListNode(0)
    dummy.next = head
    removeNth(dummy)
    return dummy.next
}

function removeNth(node: ListNode | null): void {
    if (!node || !node.next) { //NOSONAR
        return
    }
    removeNth(node.next)
    localN--

    if (localN === 0) {
        node.next = node.next?.next || null //NOSONAR
    }
}

export { removeNthFromEnd }

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