70 lines
2.1 KiB
JavaScript
70 lines
2.1 KiB
JavaScript
/*
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* Copyright 2013 AJ O'Neal
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* Copyright 2015 Tiancheng "Timothy" Gu
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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'use strict'
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/**
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* @file
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*
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* Implementation of the Fisher-Yates shuffle algorithm in JavaScript, with
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* the possibility of using a seed to ensure reproducibility.
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*
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* @module knuth-shuffle-seeded
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*/
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var randGen = require('seed-random')
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/**
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* Shuffle an array using the Fisher-Yates shuffle algorithm, aka Knuth
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* shuffle.
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*
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* Note that this function overwrites the initial array. As a result if you
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* would like to keep the original array intact, you have to copy the initial
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* array to a new array.
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*
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* Implementation derived from http://stackoverflow.com/questions/2450954/.
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*
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* @param {Array} array An array that is to be shuffled.
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* @param [seed=Math.random()] Seed for the shuffling operation. If
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* unspecified then a random value is used.
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* @return {Array} The resulting array.
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*/
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module.exports = function shuffle(array, seed) {
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var currentIndex
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, temporaryValue
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, randomIndex
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, rand
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if (seed == null) rand = randGen()
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else rand = randGen(seed)
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if (array.constructor !== Array) throw new Error('Input is not an array')
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currentIndex = array.length
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// While there remain elements to shuffle...
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while (0 !== currentIndex) {
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// Pick a remaining element...
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randomIndex = Math.floor(rand() * (currentIndex --))
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// And swap it with the current element.
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temporaryValue = array[currentIndex]
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array[currentIndex] = array[randomIndex]
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array[randomIndex] = temporaryValue
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}
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return array
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}
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