def prime_factors_ver1(num):
    """
    分解质因数: 试除法
    遍历num所有可能的因子，返回所有实际的因子
    """
    result = []
    for i in range(2, num + 1):
        s = 0
        while num % i == 0:   # 判断是否可以继续整除
            num = num / i
            s += 1
        if s > 0:   # 即可以整除i
            for k in range(s):
                result.append(i)
            if num == 1:
                return result