Add declarative version of quick sort

src/algorithms/sorting/quick-sort/QuickSortDeclarative.js

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+import Sort from '../Sort';
+
+export default class QuickDeclarativeSort extends Sort {
+  /**
+   * @param {*[]} originalArray
+   * @return {*[]}
+   */
+  sort(originalArray) {
+    if (originalArray.length < 1) {
+      return originalArray;
+    }
+    const array = [...originalArray];
+    const currentElement = array.shift();
+
+    this.callbacks.visitingCallback(currentElement);
+
+    return [
+      ...this.sort(array.filter(element => this.comparator.lessThan(element, currentElement))),
+      currentElement,
+      ...this.sort(array.filter(element => !this.comparator.lessThan(element, currentElement))),
+    ];
+  }
+}

src/algorithms/sorting/quick-sort/__test__/QuickSortDeclarative.test.js

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+import QuickSortDeclarative from '../QuickSortDeclarative';
+import {
+  equalArr,
+  notSortedArr,
+  reverseArr,
+  sortedArr,
+  SortTester,
+} from '../../SortTester';
+
+// Complexity constants.
+const SORTED_ARRAY_VISITING_COUNT = 20;
+const NOT_SORTED_ARRAY_VISITING_COUNT = 20;
+const REVERSE_SORTED_ARRAY_VISITING_COUNT = 20;
+const EQUAL_ARRAY_VISITING_COUNT = 20;
+
+describe('QuickSortDeclarative', () => {
+  it('should sort array', () => {
+    SortTester.testSort(QuickSortDeclarative);
+  });
+
+  it('should sort array with custom comparator', () => {
+    SortTester.testSortWithCustomComparator(QuickSortDeclarative);
+  });
+
+  it('should sort negative numbers', () => {
+    SortTester.testNegativeNumbersSort(QuickSortDeclarative);
+  });
+
+  it('should visit EQUAL array element specified number of times', () => {
+    SortTester.testAlgorithmTimeComplexity(
+      QuickSortDeclarative,
+      equalArr,
+      EQUAL_ARRAY_VISITING_COUNT,
+    );
+  });
+
+  it('should visit SORTED array element specified number of times', () => {
+    SortTester.testAlgorithmTimeComplexity(
+      QuickSortDeclarative,
+      sortedArr,
+      SORTED_ARRAY_VISITING_COUNT,
+    );
+  });
+
+  it('should visit NOT SORTED array element specified number of times', () => {
+    SortTester.testAlgorithmTimeComplexity(
+      QuickSortDeclarative,
+      notSortedArr,
+      NOT_SORTED_ARRAY_VISITING_COUNT,
+    );
+  });
+
+  it('should visit REVERSE SORTED array element specified number of times', () => {
+    SortTester.testAlgorithmTimeComplexity(
+      QuickSortDeclarative,
+      reverseArr,
+      REVERSE_SORTED_ARRAY_VISITING_COUNT,
+    );
+  });
+});