如何让一个函数return既是数组的索引又是数组的值？

Question

此函数计算字母在给定字符串中出现的频率并将其放入数组中（索引是字母的 ascii 数，值是计算的出现次数）。现在我需要 return 字母（它已经这样做了）和值。只是通过在线阅读，我无法弄清楚如何使用 ref 和替代方法来做到这一点。

static char MostCommonLetter(string s)
    {
        int[] occurrances = new int[255];
        for (int i = 0; i < s.Length; i++)
        {
            if (char.IsLetter(s[i]))
            {
                int ascii = (int)s[i];
                occurrances[ascii]++;
            }
        }
        char maxValue = (char)Array.IndexOf(occurrances, occurrances.Max());
        return maxValue;
    }

Answer 1

在 C# 7 及更高版本中，Value Tuples 是您的最佳选择。您可以按如下方式定义函数：

static (char letter, int occurrences) MostCommonLetter(string s)
{
    int[] occurrences = new int[255];
    for (int i = 0; i < s.Length; i++)
    {
        if (char.IsLetter(s[i]))
        {
            int ascii = (int)s[i];
            occurrances[ascii]++;
        }
    }
    char letter = (char)Array.IndexOf(occurrences, occurrences.Max());
    return (index: letter, occurrences: occurrences);
}

然后您可以像这样引用输出：

var (index, occurrences) = MostCommonLetter(yourString);

Answer 2

您可以使用 "out" 参数来 return 函数中的其他参数。

    static char MostCommonLetter(string s, out int maxOccurrance)
    {
        int[] occurrances = new int[255];
        for (int i = 0; i < s.Length; i++)
        {
            if (char.IsLetter(s[i]))
            {
                int ascii = (int)s[i];
                occurrances[ascii]++;
            }
        }

        maxOccurrance = occurrances.Max();
        char maxValue = (char)Array.IndexOf(occurrances, maxOccurrance);

        return maxValue;
    }

    //...

    // In C# 7 and above you can call it like that
    var c = MostCommonLetter("abccd", out int maxOccurrance);

    //// In older version of C# you should just declare out variable before use it
    //int maxOccurrance;
    //var c = MostCommonLetter("abccd", out maxOccurrance);

Answer 3

另一种解决方案是使用 LINQ：

string str = "Hello World!";

var result = str.GroupBy(c => c)
                .Select(group => new { Letter = group.Key, Count = group.Count() })
                .OrderByDescending(x => x.Count)
                .First();

char letter = result.Letter;
int count = result.Count;

字母='l'

计数 = 3

Answer 4

在 C# 中执行所需操作的最佳且灵活的方法是使用 struct.

以这种方式定义一个结构，并用它来同时return多个结果（一个结构甚至可以包含函数……你可以看到这些结构更轻类）：

namespace YourApp.AnyNamespace {

    // Other things

    public struct SampleName
    {
        public char mostCommon;
        public int occurancies;
    }
}

如何让一个函数return既是数组的索引又是数组的值？

How to have a function return both index and value of an array?

c#

tuples

return

ref

out