algorithm8.html

<!DOCTYPE html>
<html>
<body>


<script>

    //https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/intermediate-algorithm-scripting/dna-pairing 
    //The DNA strand is missing the pairing element. Take each character, get its pair, and return the results as a 2d array.
    //Return the provided character as the first element in each array.


    function pairElement(str) {

        var arr = str.split("");
        var newArr = [];

        for (var i=0; i<arr.length; i++) {
            if (arr[i] == "A") {
                newArr.push([arr[i],"T"])
            }
            if (arr[i] == "T") {
                newArr.push([arr[i],"A"])
            }
            if (arr[i] == "C") {
                newArr.push([arr[i],"G"])
            }
            if (arr[i] == "G") {
                newArr.push([arr[i],"C"])
            }
        }

    return newArr;
}


// solution #2
//function pairElement(str) {
//   //create object for pair lookup
//   var pairs = {
//     A: "T",
//     T: "A",
//     C: "G",
//     G: "C"
//   };
//   //split string into array of characters
//   var arr = str.split("");
//   //map character to array of character and matching pair
//   return arr.map(x => [x, pairs[x]]);
// }


//tests 

console.log(pairElement("ATCGA"));
console.log(pairElement("TTGAG"));
console.log(pairElement("CTCTA"));
console.log(pairElement("GCG"));


    </script>

</body>
</html>