feature: add go solution for leetcode 0617

Author: hzliangbin

solution/0600-0699/0617.Merge Two Binary Trees/README.md

@@ -51,8 +51,29 @@
 
 ```
 
-### **...**
-```
+### **Go**
+```go
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+func mergeTrees(t1 *TreeNode, t2 *TreeNode) *TreeNode {
+    if t1 == nil {
+        return t2
+    }
+    if t2 == nil {
+        return t1
+    }
+    t1.Val += t2.Val
+    t1.Left = mergeTrees(t1.Left, t2.Left)
+    t1.Right = mergeTrees(t1.Right, t2.Right)
+    return t1
+}
+
 
 ```
 

solution/0600-0699/0617.Merge Two Binary Trees/Solution.go

@@ -0,0 +1,20 @@
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+func mergeTrees(t1 *TreeNode, t2 *TreeNode) *TreeNode {
+    if t1 == nil {
+        return t2
+    }
+    if t2 == nil {
+        return t1
+    }
+    t1.Val += t2.Val
+    t1.Left = mergeTrees(t1.Left, t2.Left)
+    t1.Right = mergeTrees(t1.Right, t2.Right)
+    return t1
+}