拼接字符串使字典序最小

def solve(____):
    from functools import cmp_to_key
    parts = str(____).strip().split(____)
    def cmp(____):
        return -____ if a+b < b+a else (____ if a+b > b+a else ____)
    parts.sort(key=cmp_to_key(____))
    print('____'.join(____))