C#按升序和降序排序数组

Question

我编写一个方法,如果数组(数字)的元素按排序顺序,升序或降序,则返回true,如果它们不是任何排序顺序,则返回false.如果数组是升序但我不知道如何在同一方法中检查降序,我可以返回正确的布尔值.我目前有:

public static bool IsArraySorted(int[] numbers)
{
    for (int i = 1; i < numbers.Length; i++)
    {
        if (numbers[i - 1] > numbers[i])
            return false;
    }

    return true;
}

任何人都可以提供有关如何检查已排序的降序数组的帮助吗？干杯!

Answer 1

它应该是这样的:

public static bool IsArraySorted(int[] numbers)
{
    bool? ascending = null;

    for (int i = 1; i < numbers.Length; i++)
    {
        if (numbers[i - 1] != numbers[i])
        {
            bool ascending2 = numbers[i - 1] < numbers[i];

            if (ascending == null)
            {
                ascending = ascending2;
            }
            else if (ascending.Value != ascending2)
            {
                return false;
            }
        }
    }

    return true;
}

注意使用ascending变量来保存数组的"方向".它是在第一次找到两个不同的元素时初始化的.

请注意,如果需要,您甚至可以返回数组的"方向":

public static bool IsArraySorted(int[] numbers, out bool isAscending)
{
    isAscending = true;
    bool? ascending = null;

在里面 if (ascending == null)

if (ascending == null)
{
    ascending = ascending2;
    isAscending = ascending2;
}

这是基于以下内容的通用版本IEnumerable<TSource>:

public static bool IsSorted<TSource>(IEnumerable<TSource> source, out bool isAscending, Comparer<TSource> comparer = null)
{
    isAscending = true;

    if (comparer == null)
    {
        comparer = Comparer<TSource>.Default;
    }

    bool first = true;
    TSource previous = default(TSource);

    bool? ascending = null;

    foreach (TSource current in source)
    {
        if (!first)
        {
            int cmp = comparer.Compare(previous, current);

            if (cmp != 0)
            {
                bool ascending2 = cmp < 0;

                if (ascending == null)
                {
                    ascending = ascending2;
                    isAscending = ascending2;
                }
                else if (ascending.Value != ascending2)
                {
                    return false;
                }
            }
        }

        first = false;
        previous = current;
    }

    return true;
}

注意使用bool first/ TSource previous来处理i - 1(以及for循环能够"跳过"第一个元素的事实)