19. Remove Nth Node From End of List

Posted on May 9, 2025

Solution

  • 使用兩個 Pointer 間隔 n 個 node，當快的 Pointer 走到底，慢的就是答案了。
  • Time: O(N), Space: O(1)

Implementation

class Solution {
    fun removeNthFromEnd(head: ListNode?, n: Int): ListNode? {
        val dummy = ListNode()
        dummy.next = head

        var (front, back) = dummy to dummy
        repeat(n) { front = front.next }

        while (front.next != null) {
            front = front.next
            back = back.next
        }

        back.next = back.next.next
        return dummy.next
    }
}