Problem of the Day
A new programming or logic puzzle every Mon-Fri

This link has been floating around on the internet so I figured we'd make it a problem and try to solve it in 2 parts. Part one is figuring out what the regex does and part two is writing a program to generate a valid password to fit the regex.

^.*(?=.{8,})(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*$

If you really like regex puzzles give this one a try.

Comments:

• Daniel - 10 years, 7 months ago

  My last comment seems to have disappeared! :(

  Pattern means 8 characters of more with at least one number, one uppercase, and one lowercase letter.

  My C# Solution

  static string GeneratePassword(int intLength)
  {
      bool blnHasLowercase = false;
      bool blnHasUppercase = false;
      bool blnHasNumber = false;
      Dictionary<string, string> dctCharacters; 
      char[] aryChars;
      string[] aryKeys;
      string strCharacterKey;       
      byte[] aryBytes = new byte[intLength * 8];
      char[] aryPasswordChars = new char[intLength];
      new RNGCryptoServiceProvider().GetBytes(aryBytes);
      Random objRandom = new Random();
      object syncLock = new object();
      dctCharacters = new Dictionary<string, string>();
      for (int i = 0; i < intLength; i++)
      {
          dctCharacters.Clear();
          //ensure we at least get lowercase/uppercase/number in the password
          if ((intLength - i <= 3) && (!blnHasLowercase || !blnHasUppercase || !blnHasNumber))
          {
              if (blnHasLowercase == false)
                  dctCharacters.Add("Lowercase", "abcdefghijklmnopqrstuvwxyz");
              if (blnHasUppercase == false)
                  dctCharacters.Add("Uppercase", "ABCDEFGHIJKLMNOPQRSTUVWXYZ");
              if (blnHasNumber == false)
                  dctCharacters.Add("Numbers", "0123456789");
          }
          else
          {
              dctCharacters.Add("Lowercase", "abcdefghijklmnopqrstuvwxyz");
              dctCharacters.Add("Uppercase", "ABCDEFGHIJKLMNOPQRSTUVWXYZ");
              dctCharacters.Add("Numbers", "0123456789");
              dctCharacters.Add("Characters", "!£$%^&*(){}[]@~#<>,.");
          }
          aryKeys = new string[dctCharacters.Keys.Count];
          dctCharacters.Keys.CopyTo(aryKeys, 0);
          lock (syncLock)
          {
               strCharacterKey = aryKeys[objRandom.Next(0, dctCharacters.Count)];
          }
          if (strCharacterKey == "Lowercase")
              blnHasLowercase = true;
          if (strCharacterKey == "Uppercase")
              blnHasUppercase = true;
          if (strCharacterKey == "Numbers")
              blnHasNumber = true;
          aryChars = dctCharacters[strCharacterKey].Distinct().ToArray();
          aryPasswordChars[i] = aryChars[BitConverter.ToUInt64(aryBytes, i * 8) % (uint)aryChars.Length];
      }
      return new string(aryPasswordChars);
  }
  

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• Nick Krichevsky - 10 years, 7 months ago

  The purpose is to have a password with at least 8 chars and it must contain at the very least, a number, a capital letter, and a lowercase letter. My python solution.

  import random
  password = ""
  numbers = "1234567890"
  lowerCase = "abcdefghijklmnopqrstuvwxyz"
  upperCase = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
  for i in range(3):
      password += random.choice(numbers)
      password += random.choice(lowerCase)
      password += random.choice(upperCase)
  password = ''.join(random.sample(password, len(password)))
  
  print password
  

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• Daniel - 10 years, 7 months ago

  Python has some great random functions.

  reply permalink

• David - 10 years, 7 months ago

  I like how clean this looks

  I added the capability to generate a random length for the password as well as including any valid ASCII character.

  You can condense my code, at the cost of a little readability. My method to ensure meeting the required character components was to generate a string 3 characters shorter than I desired and insert the three required types of characters at randomly selected locations.

  ''' import random

  randAscii = random.randint(32,126) requiredNumber = random.randint(48,57) requiredLower = random.randint(97,122) requiredCapital = random.randint(65,90) passwordLength = random.randint(8,32)

  newPassword = str(unichr(randAscii)) while len(newPassword) < passwordLength - 3: randAscii = random.randint(32,126) newPassword += str(unichr(randAscii))

  insertPoint = random.randint(0,len(newPassword)) newPassword = newPassword[:insertPoint] + str(unichr(requiredNumber)) + newPassword[insertPoint:] insertPoint = random.randint(0,len(newPassword)) newPassword = newPassword[:insertPoint] + str(unichr(requiredLower)) + newPassword[insertPoint:] insertPoint = random.randint(0,len(newPassword)) newPassword = newPassword[:insertPoint] + str(unichr(requiredCapital)) + newPassword[insertPoint:]

  print newPassword '''

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