具有置换长度参数的javascript置换生成器 [英] javascript permutation generator with permutation length parameter

问题描述

我在那里看到了一些发电机，但它们都是平方矩阵。例如，你给它一个三个项目的列表，它将假设长度的输出也是三个。但是，我想指定项目和长度。

I've seen a few generators out there but they all make a squared matrix. For example, you give it a list of three items and it'll assume the output of the length is also three. However, I'd like to specify the items and the length.

声音就像一个简单的问题，不能相信没有可用的库。如果那里有一个经过测试的库，我想避免自己写这个。任何建议都会很棒。

Sound like an easy problem can't believe there isn't a library available for it. Would like to avoid writing this myself if there's a tested library out there. Any suggestions would be great.

我发现的例子

var list = 'abc';
perms = permutations(list);
//you cannot define the length

示例

var list = 'abc';
var length = 3;

perms = permutations(list,length);

console.log(perms);

/* output
a,a,a
a,b,c
a,b,a
a,c,a
c,a,a
...
*/

我希望能够更改长度并相应地创建排列

I would like to be able to change length and should create permutations accordingly

length = 2

a,a
a,b
b,b
b,a

length = 4

a,a,a,a 
a,a,a,b
....

推荐答案

你可以想象长度为表示插槽的数量。考虑到N是初始列表中的元素数，每个插槽都有N种可能性。因此，给定三个值 [1,2,3] ，您将总计 3 x 3 x 3 = 27 排列。

You can imagine the length as representing the number of slots. Each slot has N possibilities, given that N is the number of elements in your initial list. So given three values [1,2,3], you will have a total of 3 x 3 x 3 = 27 permutations.

这是我的尝试。包括评论！

Here's my attempt. Comments included!

var list = [1,2,3];

var getPermutations = function(list, maxLen) {
    // Copy initial values as arrays
    var perm = list.map(function(val) {
        return [val];
    });
    // Our permutation generator
    var generate = function(perm, maxLen, currLen) {
        // Reached desired length
        if (currLen === maxLen) {
            return perm;
        }
        // For each existing permutation
        for (var i = 0, len = perm.length; i < len; i++) {
            var currPerm = perm.shift();
            // Create new permutation
            for (var k = 0; k < list.length; k++) {
                perm.push(currPerm.concat(list[k]));
            }
        }
        // Recurse
        return generate(perm, maxLen, currLen + 1);
    };
    // Start with size 1 because of initial values
    return generate(perm, maxLen, 1);
};

var res = getPermutations(list, 3);
console.log(res);
console.log(res.length); // 27

小提琴

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