Intermediate Exercism • csharp

Hamming

Challenge Overview

Calculate the Hamming distance between two DNA strands.

Visit the hamming exercise on Exercism to read the full instructions and download the exercise files.

Dig Deeper

Use LINQ

LINQ

using System;
using System.Linq;

public static class Hamming
{
    public static int Distance(string strand1, string strand2)
    {
        if (strand1.Length != strand2.Length)
            throw new ArgumentException("Strands have different length");

        return strand1.Zip(strand2).Count(pair => pair.First != pair.Second);
    }
}

The first step is to check if both strings have the same length:

if (strand1.Length != strand2.Length)
    throw new ArgumentException("Strands have different length");

Once we’ve verified that, we can safely use LINQ’s Zip() (extension) method to combine both strings:

strand1.Zip(strand2)

This call returns a sequence of (char, char) tuples, the first element being (strand1[0], strand2[0]), the second (strand1[1], strand2[1]), and so on.

We then use the Count() method overload that takes a predicate to only count the tuple pairs that have different chars (meaning: the zipped strings have different characters at that index):

Count(pair => pair.First != pair.Second)

And with that, we have quite concise code that correctly calculates the hamming distance!

Use a for-loop

`for`-loop

using System;

public static class Hamming
{
    public static int Distance(string strand1, string strand2)
    {
        if (strand1.Length != strand2.Length)
            throw new ArgumentException("Strands have different length");

        var distance = 0;

        for (var i = 0; i < strand1.Length; i++)
        {
            if (strand1[i] != strand2[i])
                distance++;
        }

        return distance;
    }
}

The first step is to check if both strings have the same length:

if (strand1.Length != strand2.Length)
    throw new ArgumentException("Strands have different length");

Once we’ve verified that, we define a variable that will keep track of the hamming distance between the two strings:

var distance = 0;

We then use a for-loop to iterate over each index of the first (and second) string:

for (var i = 0; i < strand1.Length; i++)

We could equally well have used `i < strand2.Length`, as both strings are guaranteed to have the same length.

Within the loop, we can then use a simple if-statement to check if the two strings have different characters at the specified index, and if so, increment the distance by one:

if (strand1[i] != strand2[i])
    distance++;

Finally, once each index has been checked, we return the hamming distance:

return distance;

Source: Exercism csharp/hamming