问题

与提供 n 选 k 值组合的其他示例不同，我有一个包含 n 的数组，我需要得到从 0 到 n 的所有值的组合。例如：

如果我有一个数组 5,8,3,4,9，函数将返回：

0,0,0,0,0
0,0,0,0,1
...
1,1,1,1,1
1,1,1,1,2
...
5,8,3,4,9

我可以使用一个过程来找到最大值为 n 的 k 值的组合，但它提供了太多的组合（其中许多组合是无效的，我必须丢弃）：

```csharp
private static IEnumerable<IEnumerable<T>> GetCombinations<T>(IEnumerable<T> list, int length) where T : IComparable
{
    if (length == 1) return list.Select(t => new T[] { t });
    return GetCombinations(list, length - 1)
        .SelectMany(t => list.Where(o => o.CompareTo(t.Last()) >= 0),
            (t1, t2) => t1.Concat(new T[] { t2 }));
}

0,0,0,0,0
0,0,0,0,1
...
9,9,9,9,9

<details>
<summary>英文:</summary>

Unlike other examples that provide combinations of n for k values, I have an array of n and I need a combination of all values from 0 - n.  For example:

If I have an array of 5,8,3,4,9 the function would return:

0,0,0,0,0
0,0,0,0,1
...
1,1,1,1,1
1,1,1,1,2
...
5,8,3,4,9

I can accomplish this using a process to find the combinations of a max of n for k values, but it provides too many combinations (many of these combinations are invalid that I have to throw out):

private static IEnumerable<IEnumerable<T>> GetCombinations<T>(IEnumerable<T> list, int length) where T : IComparable
{
if (length == 1) return list.Select(t => new T[] { t });
return GetCombinations(list, length - 1)
.SelectMany(t => list.Where(o => o.CompareTo(t.Last()) >= 0),
(t1, t2) => t1.Concat(new T[] { t2 }));
}

0,0,0,0,0
0,0,0,0,1
...
9,9,9,9,9

</details>


# 答案1
**得分**: 0

以下是您要翻译的代码部分：

```csharp
这是一个适用于数值类型的实现：

public static IEnumerable<T[]> Combinations<T>(T[] values) where T : INumber<T>
{
    var current = new T[values.Length];

    do
    {
        yield return current.ToArray();
    }
    while (increment());

    bool increment()
    {
        for (int index = current.Length - 1; index >= 0; --index)
        {
            if (++current[index] <= values[index])
                return true;

            current[index] = default!;
        }

        return false;
    }
}

测试代码：

public static void Main()
{
    var array = new[] { 5, 8, 3, 4, 9 };

    foreach (var combination in Combinations(array))
    {
        Console.WriteLine(string.Join(", ", combination));
    }
}

然而，您的测试代码正在使用 `IComparable` - 我无法看出它如何适用于非数值的 `IComparable` 类型，例如 `string` 和 `DateTime`。

例如，对于输入数组 `{ "Tom", "Dick", "Harry" }`，会有什么含义？

public static IEnumerable<T[]> Combinations<T>(T[] values) where T: INumber<T>
{
    var current = new T[values.Length];

    do
    {
        yield return current.ToArray();
    }
    while (increment());

    bool increment()
    {
        for (int index = current.Length - 1; index >= 0; --index)
        {
            if (++current[index] <= values[index])
                return true;

            current[index] = default!;
        }

        return false;
    }
}

public static void Main()
{
    var array = new [] { 5, 8, 3, 4, 9 };

    foreach (var combination in Combinations(array))
    {
        Console.WriteLine(string.Join(", ", combination));
    }
}