计算 C# 字符串中的重复字符

Question

我是 C# 新手，正在尝试找出如何计算字符串中重复项的数量。输入和输出示例如下：

"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;
  }
}

我的方法是循环遍历字符串中的每个字符。如果以前没有见过，请将其添加到“checkedChars”堆栈中（以跟踪它）。如果已经计数，则将其添加到“dupChars”堆栈中。然而，这没有通过测试。例如：

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

另外，当我控制台出错误时，checkedChars 堆栈似乎是空的。

谁能发现我哪里出了问题吗？

Answer 1

我建议您改用 LINQ。它是一个更适合解决该问题的工具，并且可以生成更清晰的代码：

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();
    }
}

这是输出：

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

希望这可以帮助。