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Minor Performance Improvements in BitArray and Luhn Algorithm #528

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Merged
merged 6 commits into from
Sep 20, 2025
Merged

Minor Performance Improvements in BitArray and Luhn Algorithm #528

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491e355
Initial plan
Copilot Sep 18, 2025
3650304
Improve code performance and maintainability
Copilot Sep 18, 2025
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Apply suggestion from @Copilot
michaelkrisper Sep 18, 2025
24287b3
Merge pull request #1 from michaelkrisper/copilot/fix-37d4a229-559b-4…
michaelkrisper Sep 18, 2025
b7397c0
Merge branch 'master' into master
michaelkrisper Sep 18, 2025
4b3da4a
Clean up unused using directives in NysiisEncoder
michaelkrisper Sep 18, 2025
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62 changes: 31 additions & 31 deletions Algorithms/Encoders/SoundexEncoder.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,36 @@ namespace Algorithms.Encoders;
/// </summary>
public class SoundexEncoder
{
private static readonly Dictionary<char, int> CharacterMapping = new()
{
['a'] = 0,
['e'] = 0,
['i'] = 0,
['o'] = 0,
['u'] = 0,
['y'] = 0,
['h'] = 8,
['w'] = 8,
['b'] = 1,
['f'] = 1,
['p'] = 1,
['v'] = 1,
['c'] = 2,
['g'] = 2,
['j'] = 2,
['k'] = 2,
['q'] = 2,
['s'] = 2,
['x'] = 2,
['z'] = 2,
['d'] = 3,
['t'] = 3,
['l'] = 4,
['m'] = 5,
['n'] = 5,
['r'] = 6,
};

/// <summary>
/// Encodes a string using the Soundex Algorithm.
/// </summary>
Expand Down Expand Up @@ -72,36 +102,6 @@ private IEnumerable<int> CollapseDoubles(IEnumerable<int> numbers)

private int MapToNumber(char ch)
{
var mapping = new Dictionary<char, int>
{
['a'] = 0,
['e'] = 0,
['i'] = 0,
['o'] = 0,
['u'] = 0,
['y'] = 0,
['h'] = 8,
['w'] = 8,
['b'] = 1,
['f'] = 1,
['p'] = 1,
['v'] = 1,
['c'] = 2,
['g'] = 2,
['j'] = 2,
['k'] = 2,
['q'] = 2,
['s'] = 2,
['x'] = 2,
['z'] = 2,
['d'] = 3,
['t'] = 3,
['l'] = 4,
['m'] = 5,
['n'] = 5,
['r'] = 6,
};

return mapping[ch];
return CharacterMapping[ch];
}
}
38 changes: 19 additions & 19 deletions Algorithms/Other/Luhn.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -21,49 +21,49 @@ public static class Luhn
public static bool Validate(string number) => GetSum(number) % 10 == 0;

/// <summary>
/// This algorithm only finds one number.
/// This algorithm finds one missing digit.
/// In place of the unknown digit, put "x".
/// </summary>
/// <param name="number">The number in which to find the missing digit.</param>
/// <returns>Missing digit.</returns>
public static int GetLostNum(string number)
{
var lostIndex = number.Length - 1 - number.LastIndexOf("x", StringComparison.CurrentCultureIgnoreCase);
var lostNum = GetSum(number.Replace("x", "0", StringComparison.CurrentCultureIgnoreCase)) * 9 % 10;
var missingDigitIndex = number.Length - 1 - number.LastIndexOf("x", StringComparison.CurrentCultureIgnoreCase);
var checkDigit = GetSum(number.Replace("x", "0", StringComparison.CurrentCultureIgnoreCase)) * 9 % 10;

// Case 1: If the index of the lost digit is even.
if (lostIndex % 2 == 0)
// Case 1: If the index of the missing digit is even.
if (missingDigitIndex % 2 == 0)
{
return lostNum;
return checkDigit;
}

var tempLostNum = lostNum / 2;
var candidateDigit = checkDigit / 2;

// Case 2: if the index of the lost digit isn`t even and that number <= 4.
// Case 3: if the index of the lost digit isn`t even and that number > 4.
return Validate(number.Replace("x", tempLostNum.ToString())) ? tempLostNum : (lostNum + 9) / 2;
// Case 2: if the index of the missing digit is odd and the candidate is valid.
// Case 3: if the index of the missing digit is odd and we need the alternative.
return Validate(number.Replace("x", candidateDigit.ToString())) ? candidateDigit : (checkDigit + 9) / 2;
}

/// <summary>
/// Computes the sum found by the algorithm.
/// Computes the sum found by the Luhn algorithm.
/// </summary>
/// <param name="number">The number for which the sum will be found.</param>
/// <param name="number">The number for which the sum will be calculated.</param>
/// <returns>Sum.</returns>
private static int GetSum(string number)
{
var sum = 0;
for (var i = 0; i < number.Length; i++)
{
var d = number[i] - '0';
d = (i + number.Length) % 2 == 0
? 2 * d
: d;
if (d > 9)
var digit = number[i] - '0';
digit = (i + number.Length) % 2 == 0
? 2 * digit
: digit;
if (digit > 9)
{
d -= 9;
digit -= 9;
}

sum += d;
sum += digit;
}

return sum;
Expand Down
113 changes: 28 additions & 85 deletions DataStructures/BitArray.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -139,12 +139,7 @@ public sealed class BitArray : ICloneable, IEnumerator<bool>, IEnumerable<bool>
/// <param name="n">length of the array.</param>
public BitArray(int n)
{
if (n < 1)
{
field = new bool[0];
}

field = new bool[n];
field = n <= 0 ? new bool[0] : new bool[n];
}

/// <summary>
Expand Down Expand Up @@ -332,40 +327,32 @@ public void Dispose()
{
var sequence1 = one.ToString();
var sequence2 = two.ToString();
var result = string.Empty;
var tmp = string.Empty;
var result = new StringBuilder();

// for scaling of same length.
if (one.Length != two.Length)
{
var tmp = new StringBuilder();
int difference;
if (one.Length > two.Length)
{
// one is greater
difference = one.Length - two.Length;

// fills up with 0's
for (var i = 0; i < difference; i++)
{
tmp += '0';
}

tmp += two.ToString();
sequence2 = tmp;
tmp.Append('0', difference);
tmp.Append(two.ToString());
sequence2 = tmp.ToString();
}
else
{
// two is greater
difference = two.Length - one.Length;

// fills up with 0's
for (var i = 0; i < difference; i++)
{
tmp += '0';
}

tmp += one.ToString();
sequence1 = tmp;
tmp.Append('0', difference);
tmp.Append(one.ToString());
sequence1 = tmp.ToString();
}
} // end scaling

Expand All @@ -374,11 +361,10 @@ public void Dispose()

for (var i = 0; i < len; i++)
{
result += sequence1[i].Equals('0') && sequence2[i].Equals('0') ? '0' : '1';
result.Append(sequence1[i].Equals('0') && sequence2[i].Equals('0') ? '0' : '1');
}

result = result.Trim();
ans.Compile(result);
ans.Compile(result.ToString());

return ans;
}
Expand All @@ -393,22 +379,14 @@ public void Dispose()
{
var ans = new BitArray(one.Length);
var sequence = one.ToString();
var result = string.Empty;
var result = new StringBuilder(sequence.Length);

foreach (var ch in sequence)
{
if (ch == '1')
{
result += '0';
}
else
{
result += '1';
}
result.Append(ch == '1' ? '0' : '1');
}

result = result.Trim();
ans.Compile(result);
ans.Compile(result.ToString());

return ans;
}
Expand Down Expand Up @@ -444,54 +422,45 @@ public void Dispose()
{
var sequence1 = one.ToString();
var sequence2 = two.ToString();
var tmp = string.Empty;

// for scaling of same length.
if (one.Length != two.Length)
{
var tmp = new StringBuilder();
int difference;
if (one.Length > two.Length)
{
// one is greater
difference = one.Length - two.Length;

// fills up with 0's
for (var i = 0; i < difference; i++)
{
tmp += '0';
}

tmp += two.ToString();
sequence2 = tmp;
tmp.Append('0', difference);
tmp.Append(two.ToString());
sequence2 = tmp.ToString();
}
else
{
// two is greater
difference = two.Length - one.Length;

// fills up with 0's
for (var i = 0; i < difference; i++)
{
tmp += '0';
}

tmp += one.ToString();
sequence1 = tmp;
tmp.Append('0', difference);
tmp.Append(one.ToString());
sequence1 = tmp.ToString();
}
} // end scaling

var len = one.Length > two.Length ? one.Length : two.Length;
var ans = new BitArray(len);

var sb = new StringBuilder();
var sb = new StringBuilder(len);

for (var i = 0; i < len; i++)
{
_ = sb.Append(sequence1[i] == sequence2[i] ? '0' : '1');
sb.Append(sequence1[i] == sequence2[i] ? '0' : '1');
}

var result = sb.ToString().Trim();
ans.Compile(result);
ans.Compile(sb.ToString());

return ans;
}
Expand Down Expand Up @@ -575,18 +544,10 @@ public void Compile(string sequence)
ThrowIfSequenceIsInvalid(sequence);

// for appropriate scaling
var tmp = string.Empty;
if (sequence.Length < field.Length)
{
var difference = field.Length - sequence.Length;

for (var i = 0; i < difference; i++)
{
tmp += '0';
}

tmp += sequence;
sequence = tmp;
sequence = new string('0', difference) + sequence;
}

// actual compile procedure.
Expand All @@ -603,8 +564,6 @@ public void Compile(string sequence)
/// <param name="number">A positive integer number.</param>
public void Compile(int number)
{
var tmp = string.Empty;

// precondition I
if (number <= 0)
{
Expand All @@ -624,14 +583,7 @@ public void Compile(int number)
if (binaryNumber.Length < field.Length)
{
var difference = field.Length - binaryNumber.Length;

for (var i = 0; i < difference; i++)
{
tmp += '0';
}

tmp += binaryNumber;
binaryNumber = tmp;
binaryNumber = new string('0', difference) + binaryNumber;
}

// actual compile procedure.
Expand All @@ -648,8 +600,6 @@ public void Compile(int number)
/// <param name="number">A positive long integer number.</param>
public void Compile(long number)
{
var tmp = string.Empty;

// precondition I
if (number <= 0)
{
Expand All @@ -669,14 +619,7 @@ public void Compile(long number)
if (binaryNumber.Length < field.Length)
{
var difference = field.Length - binaryNumber.Length;

for (var i = 0; i < difference; i++)
{
tmp += '0';
}

tmp += binaryNumber;
binaryNumber = tmp;
binaryNumber = new string('0', difference) + binaryNumber;
}

// actual compile procedure.
Expand Down Expand Up @@ -832,7 +775,7 @@ private static void ThrowIfSequenceIsInvalid(string sequence)
}

/// <summary>
/// Utility method foir checking a given sequence contains only zeros and ones.
/// Utility method for checking a given sequence contains only zeros and ones.
/// This method will used in Constructor (sequence : string) and Compile(sequence : string).
/// </summary>
/// <param name="sequence">String sequence.</param>
Expand Down
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