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- import LinkedList from '../dataStructures/linkedList';
- /**
- * Refactored implementation of mergeSort (part of javascript-algorithms project) by Github users:
- * mgechev, AndriiHeonia and lekkas (part of javascript-algorithms project - all project contributors
- * at repository website)
- *
- * Link to repository: https://github.com/mgechev/javascript-algorithms
- */
- /**
- * Specifies a function that defines the sort order. The array is sorted according to each
- * character's Unicode code point value, according to the string conversion of each element.
- *
- * @param a {*} first compared element.
- * @param b {*} second compared element.
- * @returns {Number}
- */
- const defaultCompareFunction = function(a, b) {
- // sort lexically
- const firstValue = a.toString();
- const secondValue = b.toString();
- if (firstValue === secondValue) {
- return 0;
- } else if (firstValue < secondValue) {
- return -1;
- }
- return 1;
- };
- /**
- * Mergesort method which is recursively called for sorting the input array.
- *
- * @param {Array} array The array which should be sorted.
- * @param {Function} compareFunction Compares two items in an array. If compareFunction is not supplied,
- * elements are sorted by converting them to strings and comparing strings in Unicode code point order.
- * @param {Number} startIndex Left side of the subarray.
- * @param {Number} endIndex Right side of the subarray.
- * @returns {Array} Array with sorted subarray.
- */
- export default function mergeSort(array, compareFunction = defaultCompareFunction, startIndex = 0, endIndex = array.length) {
- if (Math.abs(endIndex - startIndex) <= 1) {
- return [];
- }
- const middleIndex = Math.ceil((startIndex + endIndex) / 2);
- mergeSort(array, compareFunction, startIndex, middleIndex);
- mergeSort(array, compareFunction, middleIndex, endIndex);
- return merge(array, compareFunction, startIndex, middleIndex, endIndex);
- }
- /**
- * Devides and sort merges two subarrays of given array
- *
- * @param {Array} array The array which subarrays should be sorted.
- * @param {Number} startIndex The start of the first subarray.
- * This subarray is with end middle - 1.
- * @param {Number} middleIndex The start of the second array.
- * @param {Number} endIndex end - 1 is the end of the second array.
- * @returns {Array} The array with sorted subarray.
- */
- export function merge(array, compareFunction, startIndex, middleIndex, endIndex) {
- const leftElements = new LinkedList();
- const rightElements = new LinkedList();
- const leftSize = middleIndex - startIndex;
- const rightSize = endIndex - middleIndex;
- const maxSize = Math.max(leftSize, rightSize);
- const size = endIndex - startIndex;
- for (let i = 0; i < maxSize; i += 1) {
- if (i < leftSize) {
- leftElements.push(array[startIndex + i]);
- }
- if (i < rightSize) {
- rightElements.push(array[middleIndex + i]);
- }
- }
- let i = 0;
- while (i < size) {
- if (leftElements.first && rightElements.first) {
- if (compareFunction(leftElements.first.data, rightElements.first.data) > 0) {
- array[startIndex + i] = rightElements.shift().data;
- } else {
- array[startIndex + i] = leftElements.shift().data;
- }
- } else if (leftElements.first) {
- array[startIndex + i] = leftElements.shift().data;
- } else {
- array[startIndex + i] = rightElements.shift().data;
- }
- i += 1;
- }
- return array;
- };
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