JavaScript隨機打亂數組順序之隨機洗牌算法

2019-11-20 09:20:02

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假如有一個數組是這樣子：

var arr1 = ["a", "b", "c", "d"];

如何隨機打亂數組順序，也即洗牌。

有一個比較廣為傳播的簡單隨機算法：

function RandomSort (a,b){ return (0.5 - Math.random()); }

實際證明上面這個并不完全隨機。

隨便一搜網上太多這種東西了，看一下stackoverflow上的一個高分回答，答案出自github上。

knuth-shuffle
The Fisher-Yates (aka Knuth) shuffle for Browser and Node.JS

下面一起看看上面說的這個算法，代碼如下：

/*jshint -W054 */(function (exports) {'use strict';// http://stackoverflow.com/questions/2450954/how-to-randomize-shuffle-a-javascript-arrayfunction shuffle(array) {var currentIndex = array.length, temporaryValue, randomIndex;// While there remain elements to shuffle...while (0 !== currentIndex) {// Pick a remaining element...randomIndex = Math.floor(Math.random() * currentIndex);currentIndex -= 1;// And swap it with the current element.temporaryValue = array[currentIndex];array[currentIndex] = array[randomIndex];array[randomIndex] = temporaryValue;}return array;}exports.knuthShuffle = shuffle;}('undefined' !== typeof exports && exports || 'undefined' !== typeof window && window || global));

作者推薦使用瀏覽器寫法：

(function () {'use strict';var a = [2,11,37,42], b;// The shuffle modifies the original array// calling a.slice(0) creates a copy, which is assigned to bb = window.knuthShuffle(a.slice(0));console.log(b);}());

Nodejs：

npm install -S knuth-shuffle(function () {'use strict';var shuffle = require('knuth-shuffle').knuthShuffle, a = [2,11,37,42], b;// The shuffle modifies the original array// calling a.slice(0) creates a copy, which is assigned to bb = shuffle(a.slice(0));console.log(b);}());

還有其它從這個算法中變形去的，比如下面這個for循環的。其它的就不說了。

/*** Randomize array element order in-place.* Using Durstenfeld shuffle algorithm.*/function shuffleArray(array) {for (var i = array.length - 1; i > 0; i--) {var j = Math.floor(Math.random() * (i + 1));var temp = array[i];array[i] = array[j];array[j] = temp;}return array;}

使用ES2015（ES6）

Array.prototype.shuffle = function() {let m = this.length, i;while (m) {i = (Math.random() * m--) >>> 0;[this[m], this[i]] = [this[i], this[m]]}return this;}

使用：