比较列表 C# 中的字符

Question

我想知道是否有任何 c# 函数可以检查字母是否存在不止一次？换句话说，我将一个字符串作为参数发送给一个函数，以检查一个字母是否存在不止一次。例如，字符串“AABDCK”应该返回“A”。有什么方法可以使用字典吗？

Answer 1

有什么方法可以使用字典吗？？

是的，遍历字符串中的每个字符并跟踪Dictionary<char, int> 中每个字符的出现次数。

Dictionary<char, int> counts = new Dictionary<char, int>();
foreach (var ch in myString)
{
    if (counts.ContainsKey(ch))
    {
        counts[ch]++;
    }
    else counts.Add(ch, 1);
} 

检查字典中值大于 1 的键。

您也可以使用 Linq 执行此操作。我不在编译器面前，但它看起来像

List<char> multipleTimes = myString
    .GroupBy(c => c)
    .Select(g => new { Character = g.Key, Count = g.Count() })
    .Where(a => a.Count > 1)
    .Select(a => a.Character)
    .ToList();

Answer 2

您可以使用 linq 来完成，查看下面的 cmets 以了解代码，例如：

public string GetLetterWithMoreOccurrences(string text)
{
   // check if the text was provided
   if (string.IsNullOrEmpty(letter))
      throw new ArgumentException("You must provide a text.", "text");

   // if it is lower than 2 chars, return the first one
   // I'm not sure if it is what you want, but let's consider it.
   if (text.Length <= 2)
      return text[0];

   // find the first letter
   var letter = text.GroupBy(c => c) // group by char
                    .Select(x => { Letter = x.Key, Total = x.Count() }) // in the group, count how many occurrences each letter has
                    .OrderByDescending(x => x.Total) // order by the total by descending
                    .First(); // get the first one

  return letter;
}

你可以检查一下：

var letter = GetLetterWithMoreOccurrences("AABDCK"); 
// should return "A"

现在，如果您想要所有出现多次的字母，您可以尝试：

public string GetLetterAllDuplicates(string text)
{
   // check if the text was provided
   if (string.IsNullOrEmpty(letter))
      throw new ArgumentException("You must provide a text.", "text");

   // if it is lower than 2 chars, return the first one
   // I'm not sure if it is what you want, but let's consider it.
   if (text.Length <= 2)
      return text[0];

   // find the first letter
   var letters = text.GroupBy(c => c) // group by char
                     // in the group, count how many occurrences each letter has
                     .Select(x => { Letter = x.Key, Total = x.Count() }) 
                      // get only the occurrences that has more than 1.. (you can change this parameter)
                     .Where(x => Total > 1) 
                     // get it as array
                     .ToArray();

  var result = string.Join(letters, "");

  return result ;
}

并使用它：

var text = GetLetterAllDuplicates("AABKCBD");
// should return "AB"

Answer 3

你可以使用：

String.IndexOf("A");

它将返回第一个 A 出现的索引。 如果它返回 -1，则没有“A”事件。

这是我不使用 IndexOf 的 LINQ 实现：

string x = "AABCDEF";
List<char> repeatedCharacters = new List<char>();
var groupsOfChars = x.GroupBy(stringCharacter => stringCharacter);
groupsOfChars
.ToList()
.ForEach(item => {
    if (item.Count() > 1) repeatedCharacters.Add(item.Key);
});

或者如果您不需要该组：

string x = "AABCDEF";
List<char> repeatedCharacters = new List<char>();
x.GroupBy(stringCharacter => stringCharacter)
.ToList()
.ForEach(item => {
    if (item.Count() > 1) repeatedCharacters.Add(item.Key);
});

然后你可以检查一下：

repeatedCharacters.ForEach(item => {
    Console.WriteLine(item.ToString());
});
//Since repeatedCharacters is an array, you can just simply do:
string stringOfRepeatedCharacters = repeatedCharacters.ToString();
//So you can easily convert the values to a String.
//[ 'A', 'B' ] is the result and it can be "AB".

Answer 4

似乎将更多的木材带入森林，但似乎有些答案不完整，或者不完全符合要求，或者非常复杂:)。

        string input = "AABZFFZDCZZK";

        //can handle null and empty string...
        var rslt =
        (string.IsNullOrEmpty(input) ? string.Empty : input)
        .GroupBy(c => c)
        .Select(gc => gc.Count() > 1 ? gc.Key : (char)0)
        .Where(c => c != (char)0)
        .OrderBy(c => c)//optional
        .Aggregate(string.Empty, (c, n) => c + n)
        ;

结果是：

        "AFZ"

问题是为返回字符串提供多次出现的字符。