617 merge two binary trees

617. 合并二叉树

go：

/**

 * Definition for a binary tree node.

 * type TreeNode struct {

 *     Val int

 *     Left *TreeNode

 *     Right *TreeNode

 * }
 */
func mergeTrees(root1 *TreeNode, root2 *TreeNode) *TreeNode {
    if root1 == nil {
        return root2
    }

    if root2 == nil {
        return root1
    }

    root1.Val += root2.Val

    root1.Left = mergeTrees(root1.Left, root2.Left)
    root1.Right = mergeTrees(root1.Right, root2.Right)

    return root1
}