如何编写O(n)程序来计算以特定数字开头和结尾的子集的数量

def countSubsets(nums):
    count = [0] * 10
    for num in nums:
        if num == nums[0]:
            count[num] += 1
        else:
            count[num] += count[num-1]
    return count

# 示例输入
nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 2, 3, 4, 5, 6, 7, 8, 9]

# 调用函数计算子集数量
subset_count = countSubsets(nums)

# 输出结果
for i in range(10):
    print(f"以数字{i}开头和结尾的子集数量为：{subset_count[i]}")