merge two sorted lists

Author: sonjh1217

merge-two-sorted-lists/sonjh1217.swift

@@ -0,0 +1,56 @@
+class Solution {
+    func mergeTwoListsIterative(_ list1: ListNode?, _ list2: ListNode?) -> ListNode? {
+        var iterList1 = list1
+        var iterList2 = list2
+        
+        var dummy = ListNode()
+        var merged = dummy
+        
+        while iterList1 != nil && iterList2 != nil,
+              let list1 = iterList1,
+              let list2 = iterList2 {
+            if list1.val < list2.val {
+                merged.next = list1
+                iterList1 = list1.next
+            } else {
+                merged.next = list2
+                iterList2 = list2.next
+            }
+            
+            guard let next = merged.next else {
+                break
+            }
+            
+            merged = next
+        }
+        
+        merged.next = iterList1 ?? iterList2
+
+        return dummy.next
+        
+        //시간복잡도 O(m+n)
+        //공간복잡도 O(1)
+    }
+    
+    func mergeTwoListsRecursion(_ list1: ListNode?, _ list2: ListNode?) -> ListNode? {
+        guard var list1 = list1 else {
+            return list2
+        }
+        
+        guard var list2 = list2 else {
+            return list1
+        }
+
+        if list1.val < list2.val {
+            list1.next = mergeTwoListsRecursion(list1.next, list2)
+            return list1
+        } else {
+            list2.next = mergeTwoListsRecursion(list1, list2.next)
+            return list2
+        }
+        
+        //시간 복잡도 O(m+n)
+        //공간 복잡도 O(m+n)
+    }
+}
+