Complete DNA pairing algorithm

Author: ahcode0919

README.md

@@ -8,7 +8,7 @@ Repository for examples of typical algorithm solutions and data structures in Ja
 
 ## Freecodecamp: Javascript Algorithms & Data Structures
 
-Algorithms from the Freecodecamp Javascript coursework
+Algorithms from the Freecodecamp Javascript algorithms and data structures certification coursework
 
 - [Basic Algorithms](https://github.com/ahcode0919/javascript-algorithm-ds/blob/master/src/fcc-basic-algorithms/fcc-basic-algorithms.md#freecodecamp-basic-algorithms)
 - [Intermediate Algorithms](https://github.com/ahcode0919/javascript-algorithm-ds/blob/master/src/fcc-intermediate-algorithms/fcc-intermediate-algorithms.md#freecodecamp-intermediate-algorithms)

src/fcc-intermediate-algorithms/dna_pairing.js

@@ -0,0 +1,23 @@
+export function pairElements(str) {
+    const pair = function(element) {
+        switch (element) {
+            case 'A':
+                return 'T';
+            case 'T':
+                return 'A';
+            case 'C':
+                return 'G';
+            case 'G':
+                return 'C';
+            default:
+                return '';
+        }
+    }
+
+    const elements = str.split('');
+    let pairs = [];
+    for (let element of elements) {
+        pairs.push([element, pair(element)]);
+    }
+    return pairs;
+}

src/fcc-intermediate-algorithms/fcc-intermediate-algorithms.md

@@ -58,7 +58,7 @@ export function destroyer(arr, ...values) {
 
 Make a function that looks through an array of objects (first argument) and returns an array of all objects that have matching name and value pairs (second argument). Each name and value pair of the source object has to be present in the object from the collection if it is to be included in the returned array.
 
-For example, if the first argument is [{ first: "Romeo", last: "Montague" }, { first: "Mercutio", last: null }, { first: "Tybalt", last: "Capulet" }], and the second argument is { last: "Capulet" }, then you must return the third object from the array (the first argument), because it contains the name and its value, that was passed on as the second argument.
+For example, if the first argument is `[{ first: "Romeo", last: "Montague" }, { first: "Mercutio", last: null }, { first: "Tybalt", last: "Capulet" }]`, and the second argument is `{ last: "Capulet" }`, then you must return the third object from the array (the first argument), because it contains the name and its value, that was passed on as the second argument.
 
 ```javascript
 export function whatIsInAName(collection, source) {
@@ -135,3 +135,41 @@ export function myReplace(str, before, after) {
     return [preInsert, after, postInsert].join('');
 }
 ```
+
+#### DNA Pairing
+
+The DNA strand is missing the pairing element. Take each character, get its pair, and return the results as a 2d array.
+
+Base pairs are a pair of `AT` and `CG`. Match the missing element to the provided character.
+
+Return the provided character as the first element in each 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.
+
+```javascript
+export function pairElements(str) {
+    const pair = function(element) {
+        switch (element) {
+            case 'A':
+                return 'T';
+            case 'T':
+                return 'A';
+            case 'C':
+                return 'G';
+            case 'G':
+                return 'C';
+            default:
+                return '';
+        }
+    }
+
+    const elements = str.split('');
+    let pairs = [];
+    for (let element of elements) {
+        pairs.push([element, pair(element)]);
+    }
+    return pairs;
+}
+```

tests/fcc-intermediate-algorithms/dna_pairing.test.js

@@ -0,0 +1,5 @@
+import { pairElements } from "../../src/fcc-intermediate-algorithms/dna_pairing";
+
+test('should pair elements', () => {
+    expect(pairElements("ATCGA")).toEqual([["A","T"],["T","A"],["C","G"],["G","C"],["A","T"]]);
+});