DNAPairing.js

// Pairs of DNA strands consist of nucleobase pairs. Base pairs are represented by the 
// characters AT and CG, which form building blocks of the DNA double helix.

// The DNA strand is missing the pairing element. Write a function to match the missing 
// base pairs for the provided DNA strand. For each character in the provided string, find 
// the base pair character. Return the results as a 2d array.

// For example, for the input GCG, return [["G", "C"], ["C","G"], ["G", "C"]]

// The character and its pair are paired up in an array, and all the arrays are grouped into 
// one encapsulating array.

// Method 1
// function pairElement(str) {
//     const matchWithBasePair = function(char) {
//       switch (char) {
//         case "A":
//           return ["A", "T"];
//         case "T":
//           return ["T", "A"];
//         case "C":
//           return ["C", "G"];
//         case "G":
//           return ["G", "C"];
//       }
//     };
  
//     const pairs = [];
//     for (let i = 0; i < str.length; i++) {
//       pairs.push(matchWithBasePair(str[i]));
//     }
  
//     return pairs;
//   }
  
//   pairElement("GCG");

function pairElement(str) {

    const pairs = {
      A: "T",
      T: "A",
      C: "G",
      G: "C"
    };

    return str
      .split("")
      .map(x => [x, pairs[x]]);
}

console.log(pairElement("GCG"));