solve problem

Author: delight010

reverse-linked-list/delight010.swift

@@ -0,0 +1,23 @@
+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 complexity O(n)
+    // Space complexity O(1)
+    func reverseList(_ head: ListNode?) -> ListNode? {
+        var reverseList: ListNode? = nil
+        var currentHead = head
+        while let node = currentHead {
+            currentHead = node.next
+            node.next = reverseList
+            reverseList = node
+        }
+        return reverseList
+    }
+}
+