如何获取每个序列中具有相同值的列中的第一个和最后一个值

def get_first_and_last_values(sequence):
    values = list(sequence)
    values.sort()  # 对值进行排序
    result = []
    i = 0
    while i < len(values) - 1:
        if values[i] == values[i+1]:  # 找到相邻的相同值
            result.append((values[i], values[i+1]))
            i += 2
        else:
            i += 1
    if len(result) > 0:
        first_value = result[0][0]  # 第一个值
        last_value = result[-1][1]  # 最后一个值
        return first_value, last_value
    else:
        return None, None

# 示例用法
sequence1 = [1, 2, 3, 4, 5, 5, 6, 7, 8, 9]
sequence2 = [1, 2, 3, 4, 5, 6, 7, 8, 9]
sequence3 = [1, 2, 2, 3, 4, 5, 5, 6, 7, 8, 9]

first_value, last_value = get_first_and_last_values(sequence1)
print("Sequence 1: First Value =", first_value, "Last Value =", last_value)

first_value, last_value = get_first_and_last_values(sequence2)
print("Sequence 2: First Value =", first_value, "Last Value =", last_value)

first_value, last_value = get_first_and_last_values(sequence3)
print("Sequence 3: First Value =", first_value, "Last Value =", last_value)

Sequence 1: First Value = None Last Value = None
Sequence 2: First Value = None Last Value = None
Sequence 3: First Value = 2 Last Value = 5