/**

 * Definition for a binary tree node.

 * function TreeNode(val) {

 *     this.val = val;

 *     this.left = this.right = null;

 * }

 */

/**

 * @param {TreeNode} root

 * @return {TreeNode}

 */

var invertTree = function(root) {

    if(root == null) return null;

    var tmpNode = root.left;

    root.left = invertTree(root.right);

    root.right = invertTree(tmpNode);

    return root;

};