solve problem

Author: delight010

remove-nth-node-from-end-of-list/delight010.swift

@@ -0,0 +1,36 @@
+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 {
+    // Time O(n)
+    // Space O(1)
+    func removeNthFromEnd(_ head: ListNode?, _ n: Int) -> ListNode? {
+        var slow: ListNode? = head
+        var fast: ListNode? = head
+        var prev: ListNode?
+        
+        for _ in 1...n {
+            fast = fast?.next
+        }
+        
+        while fast != nil {
+            prev = slow
+            slow = slow?.next
+            fast = fast?.next
+        }
+        
+        if prev != nil {
+            prev?.next = slow?.next
+        } else {
+            return head?.next
+        }
+        
+        return head
+    }
+}
+