implemented merge-sort in js with test cases (#105)

Author: ignacio-chiazzo

README.md

@@ -102,6 +102,7 @@ The solutions are located under `/LeetcodeProblems`. Each problem has a test fil
 | Algoritmhs |
 |      -     |
 | [Heap Sort](/SortingAlgorithms/heapSort.js)  |
+| [Merge Sort](/SortingAlgorithms/mergeSort.js) |
 | [Quick Sort](/SortingAlgorithms/QuickSort.js) |
 
 ### Databases

SortingAlgorithms/mergeSort.js

@@ -0,0 +1,39 @@
+function merge(leftArr, rightArr) {
+  let leftInd = 0, rightInd = 0;
+  const sortedArr = [];
+
+  while(leftInd < leftArr.length && rightInd < rightArr.length) {
+    if (leftArr[leftInd] < rightArr[rightInd]) {
+      sortedArr.push(leftArr[leftInd]);
+      leftInd++;
+    } else {
+      sortedArr.push(rightArr[rightInd]);
+      rightInd++;
+    }
+  }
+
+  // join leftover values from left array or right array
+  return sortedArr.concat(leftArr.slice(leftInd)).concat(rightArr.slice(rightInd));
+}
+
+const mergeSort = (arr) => {
+  if (arr.length <= 1) {
+    return arr;
+  }
+  
+  const mid = Math.floor(arr.length / 2);
+  const leftArr = mergeSort(arr.slice(0, mid));
+  const rightArr = mergeSort(arr.slice(mid));
+
+  return merge(leftArr, rightArr);
+};
+
+console.log(mergeSort([4,12,5,3,78,12,133,32, 1000, 4000]));
+console.log(mergeSort([14, 1, 10, 2, 3, 5, 6, 4, 7, 11, 12, 13]));
+console.log(mergeSort([]));
+console.log(mergeSort([1]));
+console.log(mergeSort([2, 1]));
+console.log(mergeSort([1,7,2,3,4,1,10,2,3,4,5]));
+console.log(mergeSort(["One Piece", "One-Punch Man", "My Hero Academia", "Jujutsu Kaisen", "Death Note", "Fullmetal Alchemist: Brotherhood", "Akame ga Kill", "Bleach", "Black Clover"]));
+
+module.exports.mergeSort = mergeSort;

SortingAlgorithmsTest/mergeSort_Test.js

@@ -0,0 +1,27 @@
+const assert = require("assert");
+const mergeSort = require("../SortingAlgorithms/mergeSort").mergeSort;
+
+var test = function () {
+  assert.deepEqual(
+    [ 3, 4, 5, 12, 12, 32, 78, 133, 1000, 4000 ],
+    mergeSort([4, 12, 5, 3, 78, 12, 133, 32, 1000, 4000])
+  );
+  
+  assert.deepEqual(
+    [1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14],
+    mergeSort([14, 1, 10, 2, 3, 5, 6, 4, 7, 11, 12, 13])
+  );
+  
+  assert.deepEqual([], mergeSort([]));
+  assert.deepEqual([1], mergeSort([1]));
+  assert.deepEqual([1, 2], mergeSort([2, 1]));
+  assert.deepEqual([1, 1, 2, 2, 3, 3, 4, 4, 5, 7, 10], mergeSort([1,7,2,3,4,1,10,2,3,4,5])
+  );
+
+  assert.deepEqual(
+    ["Akame ga Kill", "Black Clover", "Bleach", "Death Note", "Fullmetal Alchemist: Brotherhood", "Jujutsu Kaisen", "My Hero Academia", "One Piece", "One-Punch Man"],
+    mergeSort(["One Piece", "One-Punch Man", "My Hero Academia", "Jujutsu Kaisen", "Death Note", "Fullmetal Alchemist: Brotherhood", "Akame ga Kill", "Bleach", "Black Clover"])
+  );
+};
+
+module.exports.test = test;

Test.js

@@ -5,13 +5,15 @@ const fs = require("fs");
 const PROBLEMS_FOLDERS = [
   "./LeetcodeProblems/Algorithms/easy/",
   "./LeetcodeProblems/Algorithms/medium/",
-  "./LeetcodeProblems/Algorithms/hard/"
+  "./LeetcodeProblems/Algorithms/hard/",
+  "./SortingAlgorithms/"
 ];
 
 const TESTS_FOLDERS = [
   "./LeetcodeProblemsTests/Algorithms/easy/",
   "./LeetcodeProblemsTests/Algorithms/medium/",
-  "./LeetcodeProblemsTests/Algorithms/hard/"
+  "./LeetcodeProblemsTests/Algorithms/hard/",
+  "./SortingAlgorithmsTest/"
 ];
 
 const REGEX_PATTERN_HIDDEN_FILES = /(^|\/)\.[^\/\.]/g;