isSameTree = function(p, q) {
  if(p===null&&q===null){
    return true
  }
  if(p===null||q===null){
    return false
  }
  if(p.val!==q.val){
    return false
  }
  return isSameTree(p.left,q.left) && isSameTree(p.right,q.right)
}
@param {TreeNode} root
@param {TreeNode} subRoot
@return {boolean}