problems(swift): add “606. Construct String from Binary Tree”

Signed-off-by: Matej Focko <mfocko@redhat.com>

problems/swift/construct-string-from-binary-tree.swift

@@ -0,0 +1,37 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     public var val: Int
+ *     public var left: TreeNode?
+ *     public var right: TreeNode?
+ *     public init() { self.val = 0; self.left = nil; self.right = nil; }
+ *     public init(_ val: Int) { self.val = val; self.left = nil; self.right = nil; }
+ *     public init(_ val: Int, _ left: TreeNode?, _ right: TreeNode?) {
+ *         self.val = val
+ *         self.left = left
+ *         self.right = right
+ *     }
+ * }
+ */
+class Solution {
+    func tree2str(_ root: TreeNode?) -> String {
+        if let root = root {
+            let left = tree2str(root.left)
+            let right = tree2str(root.right)
+
+            var l = ""
+            if left != "" || right != "" {
+                l = "(\(left))"
+            }
+
+            var r = ""
+            if right != "" {
+                r = "(\(right))"
+            }
+
+            return "\(root.val)\(l)\(r)"
+        }
+
+        return ""
+    }
+}