Question

我是C＃的新手，正在尝试弄清楚如何计算字符串中重复项的数量。输入和输出示例为：

"indivisibility" -> 1 # 'i' occurs six times
"Indivisibilities" -> 2 # 'i' occurs seven times and 's' occurs twice
"aA11" -> 2 # 'a' and '1'
"ABBA" -> 2 # 'A' and 'B' each occur twice

到目前为止，我的代码如下：

using System;
using System.Collections;
using System.Linq;

public class Kata
{
  public static int DuplicateCount(string str)
  {
    Stack checkedChars = new Stack();
    Stack dupChars = new Stack(); 

    str = str.ToLower();

    for (int i=1; i < str.Length; i++) {
      var alreadyCounted = checkedChars.Contains(str[i]) && dupChars.Contains(str[i]);

      if (!checkedChars.Contains(str[i])) {
         checkedChars.Push(str[i]);
      } else if (checkedChars.Contains(str[i])) {
         dupChars.Push(str[i]);
      } else if (alreadyCounted) {
        break;
      }
    }
    return dupChars.Count;
  }
}

我的方法是遍历字符串中的每个字符。如果以前没有看到过，请将其添加到“ checkedChars”堆栈中（以对其进行跟踪）。如果已经计算过，请将其添加到“ dupChars”堆栈中。但是，这使测试失败。例如：

aabbcde是字符串，并且测试失败并显示：Expected: 2 But Was: 1

此外，当我解决错误时，似乎checkedChars堆栈为空。

任何人都可以发现我出了错吗？

Answer 1

我建议您改用LINQ。这是解决问题的更合适的工具，它可以使代码更简洁：

class Program
{
     static void Main(string[] args)
     {
          var word = "indivisibility";
          Console.WriteLine($"{word} has {CountDuplicates(word)} duplicates.");
          word = "Indivisibilities";
          Console.WriteLine($"{word} has {CountDuplicates(word)} duplicates.");
          word = "aA11";
          Console.WriteLine($"{word} has {CountDuplicates(word)} duplicates.");
          word = "ABBA";
          Console.WriteLine($"{word} has {CountDuplicates(word)} duplicates.");

          Console.ReadLine();
     }
     public static int CountDuplicates(string str) =>
            (from c in str.ToLower()
             group c by c
             into grp
             where grp.Count() > 1
             select grp.Key).Count();
    }
}

以下是输出：

indivisibility has 1 duplicates.
Indivisibilities has 2 duplicates.
aA11 has 2 duplicates.
ABBA has 2 duplicates.

希望这会有所帮助。

Answer 2

您需要从int i = 0开始循环，因为索引从0开始而不是1。因此，要获取第一个字符，您需要调用str[0]。

您也可以删除break，因为您的代码将永远不会碰到它，因为前两个条件是完全相反的。相反，请先检查alreadyCounted是否为真，并使用continue（而不是break，因为它会完全退出循环！）跳到下一个迭代，以避免重复计数相同的字符

Answer 3

您可以为此使用LINQ-

    var str = "aabbcde";
    var count = str.ToLower().GroupBy(x => x).Select(y => y).Where(z=>z.Count()>1).Count();

Answer 4

您还可以使用MoreLinq.CountBy：

using System;
using System.Linq;
using MoreLinq;

namespace ConsoleApp1
{
    internal class Program
    {
        private static int CountDuplicateCharacters(string s)
        {
            return s?.CountBy(c => c).Where(kvp => kvp.Value > 1).Count() ?? 0;
        }

        private static void Main(string[] args)
        {
            foreach (var s in new string[] { "indivisibility", "Indivisibilities", "aA11", "ABBA" })
            {
                Console.WriteLine(s + ": " + CountDuplicateCharacters(s));
            }
        }
    }
}

如果您不想区分大小写，则需要提供EqualityComparer作为CountBy的第二个参数。

计算C＃字符串中的重复字符

4 个答案: