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Commit bf5d7b3

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robtaussigtrekhleb
authored andcommitted
Add in-place sort to QuickSort.js (trekhleb#16)
* Add in-place sort to QuickSort.js * Fix linting errors and clean up comments * Change implementation to address lint errors * Trailing space and undefined variable * Create own class for in-place quicksort and use tests * Add trailing space at end of file * Fix placement of visitedCallback, explain itial destructuring
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‎src/algorithms/sorting/quick-sort/QuickSort.js

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@@ -5,7 +5,7 @@ export default class QuickSort extends Sort {
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// Clone original array to prevent it from modification.
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const array = [...originalArray];
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// If array has less then or equal to one elements then it is already sorted.
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// If array has less than or equal to one elements then it is already sorted.
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if (array.length <= 1) {
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return array;
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}
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import Sort from '../Sort';
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export default class QuickSortInPlace extends Sort {
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/* Sorting in place avoids unnecessary use of additional memory, but modifies input array.
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*
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* This process is difficult to describe, but much clearer with a visualization:
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* http://www.algomation.com/algorithm/quick-sort-visualization
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*/
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sort(originalArray, inputLow, inputHigh) {
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// Destructures array on initial passthrough, and then sorts in place.
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const array = inputLow === undefined ? [...originalArray] : originalArray;
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// Partition array segment and return index of last swap
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const partition = (l, h) => {
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const swap = (left, right) => {
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const tempVariable = array[left];
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array[left] = array[right];
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array[right] = tempVariable;
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};
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const pivot = array[h];
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this.callbacks.visitingCallback(array[pivot]);
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let firstRunner = l - 1;
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for (let secondRunner = l; secondRunner < h; secondRunner += 1) {
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if (this.comparator.lessThan(array[secondRunner], pivot)) {
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firstRunner += 1;
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swap(firstRunner, secondRunner);
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}
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}
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if (this.comparator.lessThan(pivot, array[firstRunner + 1])) {
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swap(firstRunner + 1, h);
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}
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return firstRunner + 1;
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};
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/*
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* While we can use a default parameter to set `low` to 0, we would
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* still have to set `high`'s default within the function as we
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* don't have access to `array.length - 1` when declaring paramaters
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*/
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const low = inputLow === undefined ? 0 : inputLow;
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const high = inputHigh === undefined ? array.length - 1 : inputHigh;
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// Base case is when low and high converge
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if (low < high) {
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const partitionIndex = partition(low, high);
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/*
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* `partition()` swaps elements of the array based on their comparison to the `hi` parameter,
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* and then returns the index where swapping is no longer necessary, which can be best thought
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* of as the pivot used to split an array in a non-in-place quicksort
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*/
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this.sort(array, low, partitionIndex - 1);
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this.sort(array, partitionIndex + 1, high);
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}
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return array;
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}
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}
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import QuickSortInPlace from '../QuickSortInPlace';
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import {
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equalArr,
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notSortedArr,
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reverseArr,
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sortedArr,
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SortTester,
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} from '../../SortTester';
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// Complexity constants.
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const SORTED_ARRAY_VISITING_COUNT = 19;
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const NOT_SORTED_ARRAY_VISITING_COUNT = 12;
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const REVERSE_SORTED_ARRAY_VISITING_COUNT = 19;
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const EQUAL_ARRAY_VISITING_COUNT = 19;
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describe('QuickSortInPlace', () => {
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it('should sort array', () => {
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SortTester.testSort(QuickSortInPlace);
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});
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it('should sort array with custom comparator', () => {
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SortTester.testSortWithCustomComparator(QuickSortInPlace);
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});
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it('should visit EQUAL array element specified number of times', () => {
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SortTester.testAlgorithmTimeComplexity(
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QuickSortInPlace,
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equalArr,
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EQUAL_ARRAY_VISITING_COUNT,
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);
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});
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it('should visit SORTED array element specified number of times', () => {
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SortTester.testAlgorithmTimeComplexity(
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QuickSortInPlace,
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sortedArr,
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SORTED_ARRAY_VISITING_COUNT,
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);
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});
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it('should visit NOT SORTED array element specified number of times', () => {
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SortTester.testAlgorithmTimeComplexity(
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QuickSortInPlace,
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notSortedArr,
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NOT_SORTED_ARRAY_VISITING_COUNT,
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);
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});
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it('should visit REVERSE SORTED array element specified number of times', () => {
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SortTester.testAlgorithmTimeComplexity(
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QuickSortInPlace,
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reverseArr,
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REVERSE_SORTED_ARRAY_VISITING_COUNT,
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);
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});
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});

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