二叉树的镜像

    import java.util.LinkedList;            public class MirrorTest      {          //递归         public void Mirror(TreeNode root)         {             if(root == null)              return;             else              {                                 TreeNode temp = root.left;//交换根节点的左右孩子                 root.left = root.right;                 root.right = temp;                 Mirror(root.left);//镜像根节点的左孩子的左右子树                 Mirror(root.right);//镜像根节点的右孩子的左右子树              }         }                  //非递归实现         public void Mirror1(TreeNode root)         {             if(root == null)             {                 return;             }           LinkedList<TreeNode> stack = new LinkedList<TreeNode>();//借助于辅助栈           TreeNode current = null;//存放出栈的栈顶元素           TreeNode temp = null;           stack.push(root);//将根元素入栈           while(!stack.isEmpty())           {              current = stack.pop();//将根元素出栈 交换根元素的左右子树              if(current.left != null || current.right != null)//若左右孩子不为空则交换左右孩子              {                  temp = current.left;                  current.left = current.right;                  current.right = temp;              }              //将根元素的左右孩子压入栈中                if(current.left != null)                  stack.push(current.left);              if(current.right != null)                  stack.push(current.right);           }                  }      }