C#升序和降序排序数组 [英] C# sorting arrays in ascending and descending order

问题描述

我很难编写一个方法，如果数组(数字)的元素按升序或降序排序，则返回true；如果数组的元素不按任何排序，则返回false.如果数组是升序的，我可以返回正确的布尔值，但是我不知道如何在同一方法中检查降序.我目前有:

I'm having trouble writing a method that returns true if the elements of an array (numbers) are in sorted order, ascending or descending, and false, if they are not in any sorted order. I can return a correct boolean value if the array is ascending but i do not know how to check for descending order as well in the same method. I currently have:

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排序降序数组的帮助吗?干杯！

Anyone able to offer help on how to check for a sorted descending array as well? Cheers!

推荐答案

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;
}

请注意使用ascending变量来保存数组的方向".首次发现两个不同的元素时会对其进行初始化.

Note the use of the ascending variable to save the "direction" of the array. It is initialized the first time two elements that are different are found.

请注意，如果需要，甚至可以返回数组的方向":

Note that if you want, you can even return the "direction" of the array:

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

和if (ascending == null)

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

这是基于IEnumerable<TSource>的通用版本:

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;
}

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

Note the use of bool first/TSource previous to handle the i - 1 (and the fact that the for cycle was able to "skip" the first element)

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