add invert binary tree solution

Author: Tessa1217

invert-binary-tree/Tessa1217.java

@@ -0,0 +1,36 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+/**
+ * 이진 트리의 root가 주어질 때 이진 트리를 뒤바꾼 후 root를 반환하세요.
+ */
+class Solution {
+    public TreeNode invertTree(TreeNode root) {
+
+        if (root == null) {
+            return root;
+        }
+
+        TreeNode current = root;
+
+        // 좌우 변경
+        TreeNode temp = current.left;
+        current.left = invertTree(current.right);
+        current.right = invertTree(temp);
+
+        return root;
+    }
+}
+