c# - 在遍历字符数组时检查两个条件

Question

在学习了C＃编程语言的基础知识/基础知识之后，我现在正在尝试解决我的第一个实际问题：写一个程序，给定一个字符串，找到其最长的子字符串，该子字符串包含至少一个大写字母，但是没有数字（然后显示此最长子字符串的长度）。对于可接受的密码，这可能是两个限定条件，例如...

我自己编写了所有代码，这意味着可能存在性能问题，但这供以后考虑。我被困在必须确保子字符串中没有数字的地方。我的代码中的注释显示了我在编写程序时的想法...

我认为首先应该检查提取的子字符串中是否存在大写字母，如果存在，则可以将该合格的子字符串存储在列表中，然后退出循环。但是，现在我想知道如何在同一子字符串中同时检查无数字的情况吗？

我试图使其保持整洁和简单（正如我所说的，我刚开始编写程序的时间超过了几行！），所以我认为做一个嵌套循环来检查每个字符是否与!char.IsNumber(letter)可能不是最佳选择。还是应该先检查是否没有数字，然后再检查是否至少有一个大写字母？

我对如何实现这两个限制感到困惑，因此希望能为解决此问题提供帮助。如果您有任何意见或建议，我也将不胜感激。例如，可以将我的子字符串存储在列表中吗？我应该制作某种字典吗？我的所有可能子字符串提取嵌套循环是否最优？

ps。有些位还没有完成。例如，我仍要执行最后一步，以找到最长的子字符串并向用户显示其长度...

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace PasswordRestriction
{
    class Program   /// Write a program that, given a string, finds the longest substring that is a valid password and returns its length.
    {
        static void Main(string[] args)
        {
            // Ask the user for an alphanumeric string.
            Console.WriteLine("Enter a string of alphanumeric values:");

            // Receive the user input as string.
            string password = Console.ReadLine();

            // Print the length of the longest qualifying substring of the user string.
            Console.WriteLine("Length of the longest qualifying substring:\n" + Solution(password).Length );

            // Prevent the console window from closing.
            Console.ReadLine();
        }


        /// The method that exracts the longest substring that is a valid password.
        /// Note that a substring is a 'contiguous' segment of a string.
        public static string Solution(string str)
        {
            // Only allow non-empty strings.
            if ( String.IsNullOrEmpty(str) )
            {
                return "";
            }
            else
            {
                // Only allow letters and digits.
                if ( str.All(char.IsLetterOrDigit) )
                {
                    // A list for containing qualifying substrings.
                    List<string> passwordList = new List<string>();

                    // Generate all possible substrings. Note that
                    // string itself is not a substring of itself!
                    for (int i = 1; i < str.Length; i++)
                    {
                        for (int j = 0; j <= (str.Length-i); j++)
                        {
                            string subStr = str.Substring(j, i);
                            Console.WriteLine(subStr);

                            bool containsNum = false;
                            bool containsUpper = false;

                            // Convert the substrings to arrays of characters with ToCharArray.
                            // This method is called on a string and returns a new character array.
                            // You can manipulate this array in-place, which you cannot do with a string.
                            char[] subStrArray = subStr.ToCharArray();

                            // Go through every character in each substring.
                            // If there is at least one uppercase letter and
                            // no digits, put the qualifying substring in a list.
                            for (int k = 0; k < subStrArray.Length; k++)
                            {
                                char letter = subStrArray[k];

                                if ( char.IsNumber(letter) )
                                {
                                    containsNum = true;
                                    break;
                                }

                                if ( char.IsUpper(letter) )
                                {
                                    containsUpper = true;
                                }

                                if ( containsUpper && (containsNum == false) && (k == subStrArray.Length - 1) )
                                {
                                    Console.WriteLine("Found the above legit password!");
                                    passwordList.Add(subStr);
                                }
                            }
                        }
                    }

                    //Find the longest stored string in the list.
                    //if (passwordList.Count != 0)
                    //{
                        string maxLength = passwordList[0];

                        foreach (string s in passwordList)
                        {
                            if (s.Length > maxLength.Length)
                            {
                                maxLength = s;
                            }
                        }
                    //}

                    // Return the qualifying substring.
                    return maxLength;
                }
                else
                {
                    return "aaaaaaaaaa";
                }
            }
        }
    }
}

Answer 1

Linq的一个好问题


不含数字-数字上的Split
至少一个大写字母-Where + Any
最长（不是最短）OrderByDescending
最长（仅一个）-FirstOrDefault


实作

string source = ....

var result = source
  .Split('0', '1', '2', '3', '4', '5', '6', '7', '8', '9')
  .Where(line => line.Any(c => c >= 'A' && c <= 'Z')) // or char.IsUpper(c)
  .OrderByDescending(line => line.Length)
  .FirstOrDefault(); // null if there're no such substrings at all