判断二叉树是否对称

class Solution {
boolean isSymmetrical(TreeNode pRoot)
{
return isSymmetrical(pRoot,pRoot);
}
boolean isSymmetrical(TreeNode pRoot1,TreeNode pRoot2){
if(pRoot1==null&&pRoot2==null)
return true;
if(pRoot1==null||pRoot2==null)
return false;
if(pRoot1.val!=pRoot2.val)
return false;
return isSymmetrical(pRoot1.left,pRoot2.right)&&isSymmetrical(pRoot1.right,pRoot2.left);
}
}