function isSymmetrical(pRoot)
{
    // write code here
    if(pRoot==null){
        return true
    }
    return judge(pRoot.left,pRoot.right)
}
function judge(left,right){
    if(left==null){return right==null}
    if(right==null){return false}
    if(left.val!=right.val){return false}
    return judge(left.left,right.right)&&judge(left.right,right.left)
}