area51/lib/collections/merge-sort.js

Experimental prototypes of alien things built in JavaScript. The bits may end up living in a different package.

"use strict";

Object.defineProperty(exports, "__esModule", {
	value: true
});
exports["default"] = mergeSort;

function merge(array, low, mid, high) {
	var i = low,
	    j = mid + 1,
	    k = low;

	var aux = [];

	for (; k <= high; k++) aux[k] = array[k];

	for (k = low; k <= high; k++) {
		if (i > mid) {
			array[k] = aux[j++];
		} else if (j > high) {
			array[k] = aux[i++];
		} else if (aux[j] < aux[i]) {
			array[k] = aux[j++];
		} else {
			array[k] = aux[i++];
		}
	}
};

function mergeWithCompare(array, low, mid, high, compare) {
	var i = low,
	    j = mid + 1,
	    k = low;

	var aux = [];
	aux.length = array.length;

	for (; k <= high; k++) aux[k] = array[k];

	for (k = low; k <= high; k++) {
		if (i > mid) {
			array[k] = aux[j++];
		} else if (j > high) {
			array[k] = aux[i++];
		} else if (compare(aux[j], aux[i]) === -1) {
			array[k] = aux[j++];
		} else {
			array[k] = aux[i++];
		}
	}
}

function performSort(array, low, high) {
	if (high <= low) return;
	var range = (high - low) / 2;
	var mid = low + Math.floor(range);
	performSort(array, low, mid);
	performSort(array, mid + 1, high);
	merge(array, low, mid, high);
}

function performSortWitCompare(array, low, high, compare) {
	if (high <= low) return;

	var range = (high - low) / 2;
	var mid = low + Math.floor(range);
	performSort(array, low, mid);
	performSort(array, mid + 1, high);
	mergeWithCompare(array, low, mid, high, compare);
}

function mergeSort(array, compare, indexStart, length) {
	indexStart = indexStart || 0;
	length = length || array.length;
	if (compare) performSortWitCompare(array, indexStart, length - 1, compare);else performSort(array, indexStart, length - 1);
}

module.exports = exports["default"];