fix mege sort issues with duplicates

Author: amejiarosario

src/algorithms/sorting/merge-sort.js

@@ -1,12 +1,12 @@
 function merge(array1, array2 = []) {
   const mergedLength = array1.length + array2.length;
-  const mergedArray = [];
+  const mergedArray = Array(mergedLength);
 
   for (let index = 0, i1 = 0, i2 = 0; index < mergedLength; index += 1) {
-    if (i2 >= array2.length || (i1 < array1.length && array1[i1] < array2[i2])) {
+    if (i2 >= array2.length || (i1 < array1.length && array1[i1] <= array2[i2])) {
       mergedArray[index] = array1[i1];
       i1 += 1;
-    } else if (i1 >= array1.length || (i2 < array2.length && array2[i2] < array1[i1])) {
+    } else if (i1 >= array1.length || (i2 < array2.length && array2[i2] <= array1[i1])) {
       mergedArray[index] = array2[i2];
       i2 += 1;
     }

src/algorithms/sorting/sorting.spec.js

@@ -35,7 +35,7 @@ sortingAlgorithms.forEach((sort) => {
       expect(sort(new Set([3, 1, 2]))).toEqual([1, 2, 3]);
     });
 
-    xit('should sort with duplicated values', () => {
+    it('should sort with duplicated values', () => {
       expect(sort([1, 3, 2, 1])).toEqual([1, 1, 2, 3]);
     });
   });