Bitwise OR on strings for large strings in c#

Question

I have two strings(with 1's and 0's) of equal lengths(<=500) and would like to apply Logical OR on these strings.

How should i approach on this. I'm working with c#.

When i consider the obvious solution, reading each char and applying OR | on them, I have to deal with apx, 250000 strings each with 500 length. this would kill my performance.

Performance is my main concern.

Thanks in advance!

Answer 1

This is fastest way:

string x="";
string y="";
StringBuilder sb = new StringBuilder(x.Length);
for (int i = 0; i < x.Length;i++ )
{
    sb.Append(x[i] == '1' || y[i] == '1' ? '1' : '0');
}
string result = sb.ToString();

Answer 2

Since it was mentioned that speed is a big factor, it would be best to use bit-wise operations.

Take a look at an ASCII table:

• The character '0' is 0x30, or 00110000 in binary.
• The character '1' is 0x31, or 00110001 in binary.

Only the last bit of the character is different. As such - we can safely say that performing a bitwise OR on the characters themselves will produce the correct character.

Another important thing we can do is do to optimize speed is to use a StringBuilder, initialized to the initial capacity of our string. Or even better: we can reuse our StringBuilder for multiple operations, although we have to ensure the StringBuilder has enough capacity.

With those optimizations considered, we can make this method:

string BinaryStringBitwiseOR(string a, string b, StringBuilder stringBuilder = null)
{
    if (a.Length != b.Length)
    {
        throw new ArgumentException("The length of given string parameters didn't match");
    }

    if (stringBuilder == null)
    {
        stringBuilder = new StringBuilder(a.Length);
    }
    else
    {
        stringBuilder.Clear().EnsureCapacity(a.Length);
    }

    for (int i = 0; i < a.Length; i++)
    {
        stringBuilder.Append((char)(a[i] | b[i]));
    }
    return stringBuilder.ToString();
}

Note that this will work for all bit-wise operations you would like to perform on your strings, you only have to modify the | operator.

Answer 3

I have two strings(with 1's and 0's) of equal lengths(<=500) and would like to apply Logical OR on these strings.

You can write a custom logical OR operator or function which takes two characters as input and produces result (e.g. if at least one of input character is '1' return '1' - otherwise return '0'). Apply this function to each character in your strings.

You can also look at this approach. You'd first need to convert each character to boolean (e.g. '1' corresponds to true), perform OR operation between two boolean values, convert back result to character '0' or '1' - depending if result of logical OR was false or true respectively. Then just append each result of this operation to each other.

Answer 4

I've found this to be faster than all proposed solutions. It combines elements from @Gediminas and @Sakura's answers, but uses a pre-initialized char[] rather than a StringBuilder.

While StringBuilder is efficient at memory management, each Append operation requires some bookkeeping of the marker, and performs more actions than only an index into an array.

string x = ...
string y = ...
char[] c = new char[x.Length];
for (int i = 0; i < x.Length; i++)
{
    c[i] = (char)(x[i] | y[i]);
}
string result = new string(c);

Answer 5

You can use a Linq query to zip and then aggregate the results:

var a = "110010";    
var b = "001110";  
var result = a.Zip(b, (i, j) => i == '1' || j == '1' ? '1' : '0')
              .Select(i => i + "").Aggregate((i, j) => i + j);

Basically, the Zip extension method, takes two sequences and apply an action on each corresponding elements of the two sequences. Then I use Select to cast from char to String and finally I aggregate the results from a sequence of strings (of "0" and "1") to a String.