JavaScript随机打乱数组顺序之随机洗牌算法

2019-11-20 09:20:02

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假如有一个数组是这样子：

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

如何随机打乱数组顺序，也即洗牌。

有一个比较广为传播的简单随机算法：

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

实际证明上面这个并不完全随机。

随便一搜网上太多这种东西了，看一下stackoverflow上的一个高分回答，答案出自github上。

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

下面一起看看上面说的这个算法，代码如下：

/*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));

作者推荐使用浏览器写法：

(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);}());

还有其它从这个算法中变形去的，比如下面这个for循环的。其它的就不说了。

/*** 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：