任意输入一个字符串，串中连续出现的相同元素构成的子序列称为平台，试建立一个类Str，求出串中最长平台的长度，并能输出最长平台的子序列。如字符串为“jkkkaabbbbbaaa”，则最长平台长度为5，子序列为“bbbbb”

为了实现这个功能，我们可以创建一个名为`Str`的类，该类包含两个方法：`find_longest_platform_length`用于计算最长平台的长度，以及`get_longest_platform_sequence`用于获取最长平台的子序列。下面是这个类的一个简单实现：

class Str:
    def __init__(self, input_string):
        self.string = input_string

    def find_longest_platform_length(self):
        platform_length = 0
        current_length = 1
        previous_char = self.string[0]
        
        for char in self.string[1:]:
            if char == previous_char:
                current_length += 1
            else:
                platform_length = max(platform_length, current_length)
                current_length = 1
            
            previous_char = char
        
        # Check for the last platform
        platform_length = max(platform_length, current_length)
        return platform_length

    def get_longest_platform_sequence(self):
        longest_platform = ""
        current_platform = self.string[0]

        for char in self.string[1:]:
            if char == current_platform:
                current_platform += char
            else:
                if len(current_platform) > len(longest_platform):
                    longest_platform = current_platform
                current_platform = char

        # Check for the last platform
        if len(current_platform) > len(longest_platform):
            longest_platform = current_platform

        return longest_platform

# 示例
input_str = "jkkkaabbbbbaaa"
str_instance = Str(input_str)
longest_length = str_instance.find_longest_platform_length()
platform_seq = str_instance.get_longest_platform_sequence()

print(f"最长平台的长度为：{longest_length}")
print(f"最长平台的子序列是：{platform_seq}")