## merge

## **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 testing are done.
- Every other rules are obviously the same than for a `program`.

### Instructions

Given two binary trees and imagine that when you put one of them to cover the other, some nodes of the two trees are overlapped while the others are not.

You need to merge them into a new binary tree. The merge rule is that if two nodes overlap, then sum node values up as the new value of the merged node. Otherwise, the NOT null node will be used as the node of new tree.

Write a function, `MergeTrees`, that returns merged tree .
Note: The merging process must start from the root nodes of both trees.

Example 1:

Input:
  
          1      
         / \  
        2   3  
       
       [1,2,3]  

          1      
         / \  
        2   3  
       
       [1,2,3]  

Merged Tree:

          2      
         / \  
        4   6  
       
       [2,4,6] 

### Expected function

```go
type TreeNode struct {
    Left    *TreeNodeL
    Val     int
    Right   *TreeNodeL
}


func MergeTrees(t1 *TreeNode, t2 *TreeNode) *TreeNode {

}
```

### Usage

Here is a possible program to test your function :

```go
package main


func main() {
  mergedTree := &TreeNode{}
  t1 := NewRandTree()
  t2 := NewRandTree()

  mergedTree = MergeTrees(t1, t2)
  printTree(mergedTree)
}
```

### Output

```console
student@ubuntu:~/[[ROOT]]/test$ go build
student@ubuntu:~/[[ROOT]]/test$ ./test
[20, 2, 3, 4, 5, 6, 6, 7, 3, 5]
student@ubuntu:~/[[ROOT]]/test$
```