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Daily Challenge #175 - Complementary DNA

#challenge

Setup

Deoxyribonucleic acid (DNA) is a chemical found in the nucleus of cells and carries the "instructions" for the development and functioning of living organisms.

In DNA strings, symbols "A" and "T" and "C" and "G" are complements of each other. Implement a function DNA_strand to match the given side of DNA with its complementary side.

Examples

DNA_strand("ATTGC") # return TAACG
DNA_strand("GTTAAC") # return CAATTG

Tests

DNA_strand("AAAA")
DNA_strand("CTACC")
DNA_strand("GTAT")

Good luck!

This challenge comes from JustyFY on CodeWars. Thank you to CodeWars, who has licensed redistribution of this challenge under the 2-Clause BSD License!

Want to propose a challenge idea for a future post? Email yo+challenge@dev.to with your suggestions!

Top comments (18)

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isaacdlyman profile image
Isaac Lyman • • Edited

This sounds like a one-liner in JS. Let's see...

const DNA_strand = str => str.split('').map(l => l === 'A' ? 'T' : l === 'T' ? 'A' : l === 'G' ? 'C' : l === 'C' ? 'G' : '').join('');
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As a bonus, any non-DNA letters will be ignored.

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vanshxrajput profile image
Vansh.c •

i am fresher can you tell me what does this ( => )operator do.

Your help is appreciated.

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isaacdlyman profile image
Isaac Lyman •

It’s an arrow function (or anonymous function).

function(a, b) {return a + b;}

Is (almost) the same as:

(a, b) => a + b

There are a few differences but most of the time they aren’t anything to worry about. If you care, this is a good overview: levelup.gitconnected.com/7-differe...

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jehielmartinez profile image
Jehiel Martinez • • Edited

JS:

function DNA_strand (str) {
    let result = '';
    for(i=0; i<str.length; i++){    
        switch (str[i]) {
            case 'A':
                result = result + 'T';
                break;
            case 'T':
                result = result + 'A';
                break;
            case 'C':
                result = result + 'G';
                break;
            case 'G':
                result = result + 'C';
                break;
            default:
                return 'Your DNA is not from this planet';
        }
    }
    return result
};
```
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ruanengelbrecht profile image
Ruan Engelbrecht •

JavaScript:

const mapping = {
  A: 'T',
  T: 'A',
  C: 'G',
  G: 'C'
};

const DNA_strand = seq =>
  seq
    .split('')
    .map(x => mapping[x])
    .join('');
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cipharius profile image
Valts Liepiņš •

Ruby keeps on pleasantly surprising me:

def DNA_strand str
    str.tr 'ATCG', 'TAGC'
end
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cipharius profile image
Valts Liepiņš •

Seems like Lua also has a neat solution:

function DNA_strand(str)
    return (str:gsub('.', {A='T',T='A',C='G',G='C'}))
end
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avalander profile image
Avalander •

Another javascript solution

const complementaryKeys = (prev, [ a, b ]) =>
  Object.assign(prev, {
    [a]: b,
    [b]: a,
  })

const pair = (...entries) => {
  const pairs = entries.reduce(complementaryKeys, {})
  return x => pairs[x] || ''
}

const dnaPairs = pair(
  [ 'A', 'T' ],
  [ 'C', 'G' ]
)

const mapStr = fn => str =>
  str.split('')
    .map(fn)
    .join('')

const dnaStrand = mapStr(dnaPairs)
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ryanbeckett profile image
Ryan Beckett • • Edited

Swift:


func DNA_strand( _ dna: String) -> String {
  let swapTable = [("A", "T"), ("T", "A"), ("C", "G"), ("G", "C")]

  return dna.map { char in
    swapTable.map { (key, value) in
      String(char) == key ? value as String : ""
    }.joined()
  }.joined()

}

I'm trying to complete these everyday for 30 days (hopefully more) - feedback more that welcome here please, thank you! Github PR

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dimitrimarion profile image
Dimitri Marion •

Javascript using Map:

const dnaMatch = new Map();
dnaMatch.set("A", "T");
dnaMatch.set("T", "A");
dnaMatch.set("C", "G");
dnaMatch.set("G", "C");

const DNA_strand = (dna) => {
    const matchedDNA = Array.prototype.map.call(dna, sym => dnaMatch.get(sym));

    return matchedDNA.join('');
};
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klaraneumannova profile image
Klára Neumannová •

PHP:

function dnaStrand(string $dnaString)
{
    $symbols = str_split($dnaString);

    $complementaryString = '';
    foreach ($symbols as $symbol) {
        switch ($symbol) {
            case 'A':
                $complementaryString .= 'T';
                break;
            case 'T':
                $complementaryString .= 'A';
                break;  
            case 'C':
                $complementaryString .= 'G';
                break;
            case 'G':
                $complementaryString .= 'C';
                break;
            default:
                return "Is '" . $symbol ."' really in your DNA?";
        }
    }

    return $complementaryString;
}

There is always a better solution, suggest one please - I'm here to learn more .)

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klaraneumannova profile image
Klára Neumannová •

OK, I found another one for PHP (7.2 and higher):

function dnaStrand(string $dnaString)
{
    $translateTable = ['A' => 'T', 'T' => 'A', 'C' => 'G', 'G' => 'C'];

    $symbols = str_split($dnaString);

    $complementaryString = '';
    foreach ($symbols as $symbol) {
        $complementaryString .= $translateTable[$symbol] ?? '';
    }

    return $complementaryString;
}
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kerldev profile image
Kyle Jones • • Edited

In Python:

def DNA_strand(strand):
    '''
    Returns the complementary strand of DNA for a given strand.
    '''
    complementary_strand = ""
    for symbol in strand:
        if symbol == 'A':
            complementary_strand += 'T'
            continue
        if symbol == 'T':
            complementary_strand += 'A'
            continue
        if symbol == 'C':
            complementary_strand += 'G'
            continue
        if symbol == 'G':
            complementary_strand += 'C'
            continue
    return complementary_strand


print(DNA_strand("ATTGC"))
print(DNA_strand("GTTAAC"))
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dbarwikowski profile image
Daniel Barwikowski •

C#

private static string DNA_strand(string dna)
{
    var sb = new StringBuilder();
    var bytes = Encoding.ASCII.GetBytes(dna);
    foreach (var b in bytes)
    {
        if ((b & 0b0000_0010) == 0)
        {
            sb.Append((char) (b ^ 0b0001_0101));
        }
        else
        {
            sb.Append((char) (b ^ 0b0000_0100));
        }
    }

    return sb.ToString();
}
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dbarwikowski profile image
Daniel Barwikowski • • Edited 
A   100 0001
T   101 0100

C   100 0011
G   100 0111

---- -|-- - this bit always changes

---| ---| - this bits only changes when ---- --|- is set to 0

View full discussion (18 comments)

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