public class Solution {
    public TreeNode invertTree(TreeNode tn){  
        if(tn == null) return null;  
        Stack<TreeNode> tnStack = new Stack<TreeNode>();  
        tnStack.push(tn);  
        while(!tnStack.isEmpty()){  
            TreeNode cur = tnStack.pop();  
            TreeNode temp = cur.left;  
            cur.left = cur.right;  
            cur.right = temp;  
            if(cur.left != null) tnStack.push(cur.left);  
            if(cur.right != null) tnStack.push(cur.right);  
        }  
        return tn;  
        //0726  
    }  
}