Adding 138. Copy List with Random Pointer in Swift

Author: Mahim1997

Diff for: swift/138-Copy-List-with-Random-Pointer.swift

@@ -0,0 +1,38 @@
+/**
+ * Definition for a Node.
+ * public class Node {
+ *     public var val: Int
+ *     public var next: Node?
+ *     public var random: Node?
+ *     public init(_ val: Int) {
+ *         self.val = val
+ *         self.next = nil
+ *    	   self.random = nil
+ *     }
+ * }
+ */
+
+class Solution {
+    // Cache of mapping from old to new nodes
+    private var mapping: [Node?: Node?] = [:]
+    
+    func copyRandomList(_ head: Node?) -> Node? {
+        // Base case: Nil node
+        guard let node = head else { return nil }
+        
+        // Mapping exists
+        guard mapping[node] == nil else { return mapping[node]! }
+        
+        // Create new node
+        let newNode = Node(node.val)
+        
+        // Add to cache (i.e. 'visit' this node)
+        mapping[node] = newNode
+        
+        // Recursive calls (preorder -> children calls)
+        newNode.next = copyRandomList(node.next)
+        newNode.random = copyRandomList(node.random)
+        
+        return newNode
+    }
+}