feat: Add solution for LeetCode problem 19

Author: WhiteHyun

remove-nth-node-from-end-of-list/WhiteHyun.swift

@@ -0,0 +1,37 @@
+//  
+//  19. Remove Nth Node From End of List
+//  https://leetcode.com/problems/remove-nth-node-from-end-of-list/description/
+//  Dale-Study
+//  
+//  Created by WhiteHyun on 2024/06/10.
+//  
+
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     public var val: Int
+ *     public var next: ListNode?
+ *     public init() { self.val = 0; self.next = nil; }
+ *     public init(_ val: Int) { self.val = val; self.next = nil; }
+ *     public init(_ val: Int, _ next: ListNode?) { self.val = val; self.next = next; }
+ * }
+ */
+class Solution {
+  func removeNthFromEnd(_ head: ListNode?, _ n: Int) -> ListNode? {
+    let answerNode = ListNode(0, head)
+    var footprintNode = head
+
+    for _ in 0 ..< n {
+      footprintNode = footprintNode?.next
+    }
+
+    var targetNode: ListNode? = answerNode
+    while footprintNode != nil {
+      targetNode = targetNode?.next
+      footprintNode = footprintNode?.next
+    }
+    targetNode?.next = targetNode?.next?.next
+
+    return answerNode.next
+  }
+}