solve

Author: sonjh1217

reverse-linked-list/sonjh1217.swift

@@ -0,0 +1,26 @@
+/**
+ * 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 {
+    // O(n) time / O(1) space
+    func reverseList(_ head: ListNode?) -> ListNode? {
+        var node = head
+        var lastNode: ListNode? = nil
+        
+        while node != nil {
+            let next = node?.next
+            node?.next = lastNode
+            lastNode = node
+            node = next
+        }
+        
+        return lastNode
+    }
+}