## invert tree

## **WARNING! VERY IMPORTANT!**

For this exercise a function will be tested **with the exam own main**. However the student **still needs** to submit a structured program:

This means that:

- The package needs to be named `package main`.
- The submitted code needs one declared function main(```func main()```) even if empty.
- The function main declared needs to **also pass** the `Restrictions Checker`(illegal functions tester). It is advised for the student to just empty the function main after its own testings are done.
- Every other rules are obviously the same than for a `program`.


### Instructions:
Write a function that takes tree and inverts(flips) and returns it.
```
type TNode struct {
    Val     int
    Left    *TNode
    Right   *TNode
}
```
Example:
```
Input:
      7
    /   \
   5     10
  / \    / \
 3   6  9  13

Output:
        7
     /    \
   10      5
  / \     / \
13   9   6   3
```
Expected function:
```
func InvertTree(root *TNode) *TNode {
}
```