Invert Binary Tree

4
/   \
2     7
/ \   / \
1   3 6   9

4
/   \
7     2
/ \   / \
9   6 3   1

public TreeNode invertTree(TreeNode root) {
if(root==null)
return null;
Queue<TreeNode> qe=new LinkedList<TreeNode>();
qe.add(root);
while(!qe.isEmpty()){
TreeNode node=qe.poll();
if(node.left!=null)
qe.add(node.left);
if(node.right!=null)
qe.add(node.right);
TreeNode t=node.left;
node.left=node.right;
node.right=t;
}
return root;
}