class Solution {
public TreeNode invertTree(TreeNode root) {
reverse(root);
return root;
}
public void reverse(TreeNode root) {
if (root == null) return ;
if (root.left == null && root.right == null) return ;
reverse(root.left);
reverse(root.right);
TreeNode t = root.left;
root.left = root.right;
root.right = t;
}
}