(LeetCode) 19. Remove Nth Node From End of List

Remove Nth Node From End of List

• Explore : Interview > Top Interveiw Questions > Easy Collection
• 분류 : Linked List
• 난이도 : Medium

Problem

Given the head of a linked list, remove the n^th 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

Solution

Exapnder

/**
 * Example:
 * var li = ListNode(5)
 * var v = li.`val`
 * Definition for singly-linked list.
 * class ListNode(var `val`: Int) {
 *     var next: ListNode? = null
 * }
 */
class Solution {
    fun removeNthFromEnd(head: ListNode?, n: Int): ListNode? {
        if (head?.next == null) {
            return null
        }

        var first = head
        var current = head

        var count = 0

        while (count < n) {
            current = current?.next
            count++
        }

        while (current?.next != null) {
            first = first?.next
            current = current?.next
        }

        if (first == head && current == null) {
            return first.next
        }
        first?.next = first?.next?.next
        return head
    }
}

Point of Thinking

• 노드가 하나면 바로 null 반환처리
• n까지 index를 카운트한뒤 해당 index의 노드만 제거한 뒤 반환