problems(swift): add “94. Binary Tree Inorder Traversal”

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

problems/swift/binary-tree-inorder-traversal.swift

@@ -0,0 +1,30 @@
+/**
+ * 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 inorderTraversal(_ root: TreeNode?, _ values: inout [Int]) {
+        if let root = root {
+            inorderTraversal(root.left, &values)
+            values.append(root.val)
+            inorderTraversal(root.right, &values)
+        }
+    }
+
+    func inorderTraversal(_ root: TreeNode?) -> [Int] {
+        var traversal: [Int] = []
+        inorderTraversal(root, &traversal)
+        return traversal
+    }
+}