gaozhidf

ids = [9, 8, 1, 2, 7, 3]
results = Model.objects.filter(id__in=ids).extra(
    select={'manual': 'FIELD(id,%s)' % ','.join(map(str, ids))},
    order_by=['manual']
)

gaozhidf

class Node(object):

    def __init__(self, val, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

def max_of_tree(root):
    if not root:
        return 0