c# - Which one is faster? Regex or EndsWith?

Question

What would be faster?

public String Roll()
{
    Random rnd = new Random();
    int roll = rnd.Next(1, 100000);
    if (Regex.IsMatch(roll.ToString(), @"(.)1{1,}$"))
    {
        return "doubles";
    }
    return "none";
}

Or

public String Roll()
{
    Random rnd = new Random();
    int roll = rnd.Next(1, 100000);
    if (roll.ToString().EndsWith("11") || roll.ToString().EndsWith("22")  || roll.ToString().EndsWith("33")  || roll.ToString().EndsWith("44")  || roll.ToString().EndsWith("55")  || roll.ToString().EndsWith("66")  || roll.ToString().EndsWith("77")  || roll.ToString().EndsWith("88")  || roll.ToString().EndsWith("99")  || roll.ToString().EndsWith("00"))
    {
        return "doubles";
    }
    return "none";
}

I'm currently using a really long if-statement list full with regexes to check if an int ends with doubles, triples, quads, quints, etc... so I would like to know which one is faster before I change all of it.

Answer 1

In your particular case, Regex is actually faster... but it is likely because you use EndsWith with many OR and redundant ToString(). If you simplify the logic, simple string operation will likely be faster.

---

Here is the performance summary for text processing - from the fastest to the slowest (10 millions loop [Prefer/Non-Prefer 32-bit] - rank is ordered based on the fastest of the two):

1. Large Lookup Fast Random UInt (not counted for bounty): 219/273 ms - Mine, improved from Evk's
2. Large Lookup Optimized Random: 228/273 ms - Ivan Stoev's Alternate Solution
3. Large Lookup Fast Random: 238/294 ms - Evk's Alternative Solution

4. Large Lookup Parameterless Random: 248/287 ms - Thomas Ayoub

   There are few notes I want to make on this solution (based on the comments below it):

   1. This solution introduces 0.0039% bias towards small numbers (< 100000) (ref: Eric Lippert's blog post, linked by Lucas Trzesniewski)
   2. Does not generate the same number sequence as others while being tested (ref: Michael Liu's comment) - since it changes the way to use Random (from Random.Next(int) to Random.Next()), which is used for the testing itself.
      
      

   While the testing cannot be performed with the exact same number sequence for this method as for the rests (as mentioned by Phil1970), I have two points to make:

   1. Some might be interested to look at the implement of Random.Next() vs Random.Next(int) to understand why this solution will still be faster even if the same sequence of numbers are used.
   2. The use of Random in the real case itself will (most of the time) not assume the number sequence to be the same (or predictable) - It is only for testing our method we want the Random sequence to be identical (for fair unit testing purpose). The expected faster result for this method cannot be fully derived from the testing result alone, but by also looking at the Next() vs Next(int) implementation.

5. Large Look-up: 320/284 ms - Evk

6. Fastest Optimized Random Modded: 286/333 ms Ivan Stoev
7. Lookup Optimized Modded: 315/329 ms - Corak
8. Optimized Modded: 471/330 ms - Stian Standahl
9. Optimized Modded + Constant: 472/337 - Gjermund Gr?neng
10. Fastest Optimized Modded: 345/340 ms - Gjermund Gr?neng
11. Modded: 496/370 ms - Corak + possibly Alexei Levenkov
12. Numbers: 537/408 ms - Alois Kraus
13. Simple: 1668/1176 ms - Mine
14. HashSet Contains: 2138/1609 ms - Dandré
15. List Contains: 3013/2465 ms - Another Mine
16. Compiled Regex: 8956/7675 ms - Radin Gospodinov
17. Regex: 15032/16640 ms - OP's Solution 1
18. EndsWith: 24763/20702 ms - OP's Solution 2

---

Here are my simple test cases:

Random rnd = new Random(10000);
FastRandom fastRnd = new FastRandom(10000);

//OP's Solution 2
public String RollRegex() {
    int roll = rnd.Next(1, 100000);
    if (Regex.IsMatch(roll.ToString(), @"(.)1{1,}$")) {
        return "doubles";
    } else {
        return "none";
    }
}

//Radin Gospodinov's Solution
Regex optionRegex = new Regex(@"(.)1{1,}$", RegexOptions.Compiled);
public String RollOptionRegex() {
    int roll = rnd.Next(1, 100000);
    string rollString = roll.ToString();
    if (optionRegex.IsMatch(roll.ToString())) {
        return "doubles";
    } else {
        return "none";
    }
}

//OP's Solution 1
public String RollEndsWith() {
    int roll = rnd.Next(1, 100000);
    if (roll.ToString().EndsWith("11") || roll.ToString().EndsWith("22") || roll.ToString().EndsWith("33") || roll.ToString().EndsWith("44") || roll.ToString().EndsWith("55") || roll.ToString().EndsWith("66") || roll.ToString().EndsWith("77") || roll.ToString().EndsWith("88") || roll.ToString().EndsWith("99") || roll.ToString().EndsWith("00")) {
        return "doubles";
    } else {
        return "none";
    }
}

//My Solution   
public String RollSimple() {
    int roll = rnd.Next(1, 100000);
    string rollString = roll.ToString();
    return roll > 10 && rollString[rollString.Length - 1] == rollString[rollString.Length - 2] ?
        "doubles" : "none";
}

//My Other Solution
List<string> doubles = new List<string>() { "00", "11", "22", "33", "44", "55", "66", "77", "88", "99" };
public String RollAnotherSimple() {
    int roll = rnd.Next(1, 100000);
    string rollString = roll.ToString();
    return rollString.Length > 1 && doubles.Contains(rollString.Substring(rollString.Length - 2)) ?
        "doubles" : "none";
}

//Dandré's Solution
HashSet<string> doublesHashset = new HashSet<string>() { "00", "11", "22", "33", "44", "55", "66", "77", "88", "99" };
public String RollSimpleHashSet() {
    int roll = rnd.Next(1, 100000);
    string rollString = roll.ToString();
    return rollString.Length > 1 && doublesHashset.Contains(rollString.Substring(rollString.Length - 2)) ?
        "doubles" : "none";
}

//Corak's Solution - hinted by Alexei Levenkov too
public string RollModded() { int roll = rnd.Next(1, 100000); return roll % 100 % 11 == 0 ? "doubles" : "none"; }

//Stian Standahl optimizes modded solution
public string RollOptimizedModded() { return rnd.Next(1, 100000) % 100 % 11 == 0 ? "doubles" : "none"; }

//Gjermund Gr?neng's method with constant addition
private const string CONST_DOUBLES = "doubles";
private const string CONST_NONE = "none";
public string RollOptimizedModdedConst() { return rnd.Next(1, 100000) % 100 % 11 == 0 ? CONST_DOUBLES : CONST_NONE; }

//Gjermund Gr?neng's method after optimizing the Random (The fastest!)
public string FastestOptimizedModded() { return (rnd.Next(99999) + 1) % 100 % 11 == 0 ? CONST_DOUBLES : CONST_NONE; }

//Corak's Solution, added on Gjermund Gr?neng's
private readonly string[] Lookup = { "doubles", "none", "none", "none", "none", "none", "none", "none", "none", "none", "none" };
public string RollLookupOptimizedModded() { return Lookup[(rnd.Next(99999) + 1) % 100 % 11]; }

//Evk's Solution, large Lookup
private string[] LargeLookup;
private void InitLargeLookup() {
    LargeLookup = new string[100000];
    for (int i = 0; i < 100000; i++) {
        LargeLookup[i] = i % 100 % 11 == 0 ? "doubles" : "none";
    }
}
public string RollLargeLookup() { return LargeLookup[rnd.Next(99999) + 1]; }

//Thomas Ayoub's Solution
public string RollLargeLookupParameterlessRandom() { return LargeLookup[rnd.Next() % 100000]; }

//Alois Kraus's Solution
public string RollNumbers() {
    int roll = rnd.Next(1, 100000);
    int lastDigit = roll % 10;
    int secondLastDigit = (roll / 10) % 10;

    if (lastDigit == secondLastDigit) {
        return "doubles";
    } else {
        return "none";
    }
}

//Ivan Stoev's Solution
public string FastestOptimizedRandomModded() {
    return ((int)(rnd.Next() * (99999.0 / int.MaxValue)) + 1) % 100 % 11 == 0 ? CONST_DOUBLES : CONST_NONE;
}

//Ivan Stoev's Alternate Solution
public string RollLargeLookupOptimizedRandom() {
    return LargeLookup[(int)(rnd.Next() * (99999.0 / int.MaxValue))];
}

//Evk's Solution using FastRandom
public string RollLargeLookupFastRandom() {
    return LargeLookup[fastRnd.Next(99999) + 1];
}

//My Own Test, using FastRandom + NextUInt
public string RollLargeLookupFastRandomUInt() {
    return LargeLookup[fastRnd.NextUInt() % 99999 + 1];
}

---

The additional FastRandom class:

//FastRandom's part used for the testing
public class FastRandom {
    // The +1 ensures NextDouble doesn't generate 1.0
    const double REAL_UNIT_INT = 1.0 / ((double)int.MaxValue + 1.0);
    const double REAL_UNIT_UINT = 1.0 / ((double)uint.MaxValue + 1.0);
    const uint Y = 842502087, Z = 3579807591, W = 273326509;

    uint x, y, z, w;

    #region Constructors

    /// <summary>
    /// Initialises a new instance using time dependent seed.
    /// </summary>
    public FastRandom() {
        // Initialise using the system tick count.
        Reinitialise((int)Environment.TickCount);
    }

    /// <summary>
    /// Initialises a new instance using an int value as seed.
    /// This constructor signature is provided to maintain compatibility with
    /// System.Random
    /// </summary>
    public FastRandom(int seed) {
        Reinitialise(seed);
    }

    #endregion

    #region Public Methods [Reinitialisation]

    /// <summary>
    /// Reinitialises using an int value as a seed.
    /// </summary>
    /// <param name="seed"></param>
    public void Reinitialise(int seed) {
        // The only stipulation stated for the xorshift RNG is that at least one of
        // the seeds x,y,z,w is non-zero. We fulfill that requirement by only allowing
        // resetting of the x seed
        x = (uint)seed;
        y = Y;
        z = Z;
        w = W;
    }

    #endregion

    #region Public Methods [System.Random functionally equivalent methods]

    /// <summary>
    /// Generates a random int over the range 0 to int.MaxValue-1.
    /// MaxValue is not generated in order to remain functionally equivalent to System.Random.Next().
    /// This does slightly eat into some of the performance gain over System.Random, but not much.
    /// For better performance see:
    /// 
    /// Cal