Python字符串中最长的字符序列

def longest_sequence(string):
    max_length = 0
    start_index = 0
    current_length = 1

    for i in range(1, len(string)):
        if string[i] == string[i-1]:
            current_length += 1
        else:
            if current_length > max_length:
                max_length = current_length
                start_index = i - max_length
            current_length = 1

    if current_length > max_length:
        max_length = current_length
        start_index = len(string) - max_length

    return string[start_index:start_index+max_length]

# 示例用法
string = "aabbbccccddddd"
longest_seq = longest_sequence(string)
print(longest_seq)