Add mergeSort

src/sort/merge/mergeSort.spec.ts

@@ -0,0 +1,39 @@
+import mergeSort from './mergeSort';
+
+const sortLowToHigh = (a: number, b: number): boolean => (a > b);
+const sortHighToLow = (a: number, b: number): boolean => (a < b);
+
+describe('Merge sort', () => {
+  it('should return an empty array when the array for sorting is empty', () => {
+    const arrayToSort: number[] = [];
+    const expectedArray: number[] = [];
+    expect(mergeSort(arrayToSort, sortLowToHigh))
+      .toEqual(expectedArray);
+  });
+
+  it('should return an array with the element', () => {
+    const arrayToSort: number[] = [14];
+    const expectedArray: number[] = [14];
+    expect(mergeSort(arrayToSort, sortLowToHigh))
+      .toEqual(expectedArray);
+  });
+
+  it('should return an array with two elements sorted from lowest to highest', () => {
+    const arrayToSort = [65, 43];
+    const expectedArray = [43, 65];
+    expect(mergeSort(arrayToSort, sortLowToHigh))
+      .toEqual(expectedArray);
+  });
+
+  it('should return an array sorted from lowest to highest', () => {
+    const arrayToSort = [43, 65, 44, 12, 67, 1, 9, 33, 21];
+    const expectedArray = [1, 9, 12, 21, 33, 43, 44, 65, 67];
+    expect(mergeSort(arrayToSort, sortLowToHigh)).toEqual(expectedArray);
+  });
+
+  it('should return an array sorted from highest to lowest', () => {
+    const arrayToSort = [43, 65, 44, 12, 67, 1, 9, 33, 21];
+    const expectedArray = [67, 65, 44, 43, 33, 21, 12, 9, 1];
+    expect(mergeSort(arrayToSort, sortHighToLow)).toEqual(expectedArray);
+  });
+});

src/sort/merge/mergeSort.ts

@@ -0,0 +1,42 @@
+interface CompareFunction {
+  (a: number, b: number): boolean;
+}
+
+function merge(a: number[], b: number[], compareFunction: CompareFunction) {
+  const arrayC: number[] = [];
+  while (a[0] && b[0]) {
+    if (compareFunction(a[0], b[0])) {
+      arrayC.push((b).shift() as number);
+    } else {
+      arrayC.push(a.shift() as number);
+    }
+  }
+  while (a[0]) {
+    arrayC.push(a.shift() as number);
+  }
+  while (b[0]) {
+    arrayC.push(b.shift() as number);
+  }
+  return arrayC;
+}
+
+export default function mergeSort(array: number[], compareFunction:CompareFunction): number[] {
+  if (!array.length) {
+    return [];
+  }
+  const introducedArray = array;
+  if (introducedArray.length === 1) {
+    return introducedArray;
+  }
+  let arrayA: number[] = [];
+  for (let i = 0; i < Math.trunc(introducedArray.length / 2); i += 1) {
+    arrayA.push(introducedArray[i]);
+  }
+  arrayA = mergeSort(arrayA, compareFunction);
+  let arrayB: number[] = [];
+  for (let i = Math.trunc(introducedArray.length / 2); i < introducedArray.length; i += 1) {
+    arrayB.push(introducedArray[i]);
+  }
+  arrayB = mergeSort(arrayB, compareFunction);
+  return merge(arrayA, arrayB, compareFunction);
+}