比較列表C＃中的char

Question

我想知道是否有任何c＃函數檢查字母是否存在然后才存在？ 換句話說，我將一個字符串作為參數發送給函數，以檢查一個字母是否存在多次。 例如，字符串“ AABDCK”應返回“ A”。 有什么方法可以使用字典嗎？

Answer 1

有什么方法可以使用字典嗎？

是，遍歷字符串中的每個字符，並跟蹤Dictionary<char, int>中每個字符的出現次數。

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

檢查字典中值大於1的鍵。

您也可以使用Linq執行此操作。 我不在編譯器的前面，但是看起來像

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進行操作，查看下面的注釋以了解代碼，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;
}

您可以檢查：

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

現在，如果您希望所有出現多個字母的字母，可以嘗試：

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 ;
}

並使用它：

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

Answer 3

您可以使用：

String.IndexOf("A");

它將返回第一次出現的索引。 如果返回-1，則不會出現“ A”事件。

這是我的不使用IndexOf的LINQ實現：

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，如果您不需要該組：

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

然后您可以檢查它：

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

似乎要把更多的木材帶入森林，但似乎有些答案不完整或不完全符合要求，或者太復雜了：）。

        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)
        ;

結果是：

        "AFZ"

問題是要向后字符串提供多次出現的字符。