翻转二叉树 ​

var invertTree = function(root) {
    if(root==null) return root;
    swapChildren(root);     
    invertTree(root.left);
    invertTree(root.right);
    return root;
}
    
var swapChildren = function(root) {
    let tmp = root.left;
    root.left = root.right;
    root.right = tmp;
}