尝试从列表中返回唯一元素

def find_unique_element(lst):
    # 方法1：使用哈希表
    count = {}
    for element in lst:
        count[element] = count.get(element, 0) + 1

    unique_elements = []
    for element, freq in count.items():
        if freq == 1:
            unique_elements.append(element)

    return unique_elements

    # 方法2：使用集合
    # unique_elements = set(lst)
    # for element in lst:
    #     if lst.count(element) > 1:
    #         unique_elements.remove(element)
    # return list(unique_elements)

    # 方法3：使用列表推导式和count()
    # return [element for element in lst if lst.count(element) == 1]

# 示例用法
lst = [1, 2, 3, 4, 5, 1, 2, 3, 4]
unique_elements = find_unique_element(lst)
print(unique_elements)  # 输出: [5]