Combining these two Regular Expressions into one

Question

I have the following in C#:

public static bool IsAlphaAndNumeric(string s)
{
    return Regex.IsMatch(s, @"[a-zA-Z]+") 
        && Regex.IsMatch(s, @"\d+");
}

I want to check if parameter s contains at least one alphabetical character and one digit and I wrote the above method to do so.

But is there a way I can combine the two regular expressions ("[a-zA-Z]+" and "\d+") into one ?

Answer 1

@"^(?=.*[a-zA-Z])(?=.*\d)"

 ^  # From the begining of the string
 (?=.*[a-zA-Z]) # look forward for any number of chars followed by a letter, don't advance pointer
 (?=.*\d) # look forward for any number of chars followed by a digit)

Uses two positive lookaheads to ensure it finds one letter, and one number before succeding. You add the ^ to only try looking forward once, from the start of the string. Otherwise, the regexp engine would try to match at every point in the string.

Answer 2

For C# with LINQ:

return s.Any(Char.IsDigit) && s.Any(Char.IsLetter);

Answer 3

You could use [a-zA-Z].*[0-9]|[0-9].*[a-zA-Z], but I'd only recommend it if the system you were using only accepted a single regex. I can't imagine this would be more efficient than two simple patterns without alternation.

Answer 4

Its not exactly what you want but let say i have more time. Following should work faster than regex.

    static bool IsAlphaAndNumeric(string str) {
        bool hasDigits = false;
        bool  hasLetters=false;

        foreach (char c in str) {
            bool isDigit = char.IsDigit(c);
            bool isLetter = char.IsLetter(c);
            if (!(isDigit | isLetter))
                return false;
            hasDigits |= isDigit;
            hasLetters |= isLetter;
        }
        return hasDigits && hasLetters;
    }

Why its fast let check it out. Following is the test string generator. It generate 1/3 of set completly correct string and 2/3 ad incorrect. In 2/3 1/2 is all alphs and other half is all digits.

    static IEnumerable<string> GenerateTest(int minChars, int maxChars, int setSize) {
        string letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
        string numbers = "0123456789";            
        Random rnd = new Random();
        int maxStrLength = maxChars-minChars;
        float probablityOfLetter = 0.0f;
        float probablityInc = 1.0f / setSize;
        for (int i = 0; i < setSize; i++) {
            probablityOfLetter = probablityOfLetter + probablityInc;
            int length = minChars + rnd.Next() % maxStrLength;
            char[] str = new char[length];
            for (int w = 0; w < length; w++) {
                if (probablityOfLetter < rnd.NextDouble())
                    str[w] = letters[rnd.Next() % letters.Length];
                else 
                    str[w] = numbers[rnd.Next() % numbers.Length];                    
            }
            yield return new string(str);
        }
    }

Following is darin two solution. One has compiled and other is noncompiled version.

class DarinDimitrovSolution
{
    const string regExpression = @"^(?=.*[a-z])(?=.*[A-Z])(?=.*\d).+$";
    private static readonly Regex _regex = new Regex(
        regExpression, RegexOptions.Compiled);

    public static bool IsAlphaAndNumeric_1(string s) {
        return _regex.IsMatch(s);
    }
    public static bool IsAlphaAndNumeric_0(string s) {
        return Regex.IsMatch(s, regExpression);
    }

Following is the main of the test loop

    static void Main(string[] args) {

        int minChars = 3;
        int maxChars = 13;
        int testSetSize = 5000;
        DateTime start = DateTime.Now;
        foreach (string testStr in
            GenerateTest(minChars, maxChars, testSetSize)) {
            IsAlphaNumeric(testStr);
        }
        Console.WriteLine("My solution : {0}", (DateTime.Now - start).ToString());

        start = DateTime.Now;
        foreach (string testStr in
            GenerateTest(minChars, maxChars, testSetSize)) {
            DarinDimitrovSolution.IsAlphaAndNumeric_0(testStr);
        }
        Console.WriteLine("DarinDimitrov  1 : {0}", (DateTime.Now - start).ToString());

        start = DateTime.Now;
        foreach (string testStr in
            GenerateTest(minChars, maxChars, testSetSize)) {
            DarinDimitrovSolution.IsAlphaAndNumeric_1(testStr);
        }
        Console.WriteLine("DarinDimitrov(compiled) 2 : {0}", (DateTime.Now - start).ToString());

        Console.ReadKey();
    }

Following is results

My solution : 00:00:00.0170017    (Gold)
DarinDimitrov  1 : 00:00:00.0320032  (Silver medal) 
DarinDimitrov(compiled) 2 : 00:00:00.0440044   (Gold)

So the first solution was the best. Some more result in release mode and following spec

   int minChars = 20;
   int maxChars = 50;
   int testSetSize = 100000;

My solution : 00:00:00.4060406
DarinDimitrov  1 : 00:00:00.7400740
DarinDimitrov(compiled) 2 : 00:00:00.3410341 (now that very fast)

I checked again with RegexOptions.IgnoreCase flag. rest of param same as above

My solution : 00:00:00.4290429 (almost same as before)
DarinDimitrov  1 : 00:00:00.9700970 (it have slowed down )
DarinDimitrov(compiled) 2 : 00:00:00.8440844 ( this as well still fast but look at .3 in last result)

After gnarf mention that there was a problem with my algo it was checking if string only consist of letter and digits so i change it and now it check that string show have atleast one char and one digit.

    static bool IsAlphaNumeric(string str) {
        bool hasDigits = false;
        bool hasLetters = false;

        foreach (char c in str) {
            hasDigits |= char.IsDigit(c);
            hasLetters |= char.IsLetter(c);
            if (hasDigits && hasLetters)
                return true;
        }
        return false;
    }

Results

My solution : 00:00:00.3900390 (Goody Gold Medal)
DarinDimitrov  1 : 00:00:00.9740974 (Bronze Medal)
DarinDimitrov(compiled) 2 : 00:00:00.8230823 (Silver)

Mine is fast by a big factor.