Add solution 617

Author: vulgur

Diff for: 617_MergeTwoBinaryTrees.swift

@@ -0,0 +1,28 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     public var val: Int
+ *     public var left: TreeNode?
+ *     public var right: TreeNode?
+ *     public init(_ val: Int) {
+ *         self.val = val
+ *         self.left = nil
+ *         self.right = nil
+ *     }
+ * }
+ */
+class Solution {
+    func mergeTrees(_ t1: TreeNode?, _ t2: TreeNode?) -> TreeNode? {
+        if let t1 = t1, let t2 = t2  {
+            var mergedNode = TreeNode(t1.val+t2.val)
+            mergedNode.left = mergeTrees(t1.left, t2.left)
+            mergedNode.right = mergeTrees(t1.right, t2.right)
+            return mergedNode
+        } else if let t1 = t1 {
+            return t1
+        } else if let t2 = t2 {
+            return t2
+        }
+        return nil
+    }
+}