Recursively Concatenate Strings in Array JavaScript

Question

I have an array of type String in Javascript. Eg: ["ab", "cd", "ef", "gh"] This array is not fixed & is alphabetically ordered.

I want an output like this:

ab
abcd
abef
abgh
abcdef
abcdgh
abefgh
abcdefgh

cd
cdef
cdgh
cdefgh

ef
efgh

Please show us your effort first. Do you have some code where you tried to address your problem? — Robin Ellerkmann
– Robin Ellerkmann, Commented Feb 18, 2015 at 11:19

Bergi · Accepted Answer · 2015-02-18 14:04:48Z

2

Use this for creating the power set of x:

function power(x) {
    var r = [""], // start with empty set/string
        l = 1;
    for (var i=0; i<x.length; l=1<<++i) // OK, l is just r[i].length, but this looks nicer :)
        for (var j=0; j<l; j++) {
            r.push(r[j].slice(0)); // copy
            r[j] += x[i];
        }
    return r;
}

Usage:

> power(["ab", "cd", "ef", "gh"])
["abcdefgh", "cdefgh", "abefgh", "efgh", "abcdgh", "cdgh", "abgh", "gh", "abcdef", "cdef", "abef", "ef", "abcd", "cd", "ab", ""]

answered Feb 18, 2015 at 14:04

Bergi

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1 Comment

Varun R Over a year ago

Thanks a lot Bergi. Power set did not come to my mind :P

OlliM · Accepted Answer · 2015-02-18 12:03:58Z

0

I agree with robin that you should try yourself first, but here it is (with help from lodash library):

function combos(arr) {
  if(arr.length <= 1) return arr
  return _.flatten(arr.map(function(key, index) {
    return [[key]].concat(
      combos(arr.slice(index+1))
      .map(function(combo) { return [key].concat(combo) })
    )
  }))
}

console.log(
  combos(["a", "b", "c", "d"])
  .map(function(arr) { return arr.join("")})
 )

http://jsbin.com/caxowuwuki/3/edit

answered Feb 18, 2015 at 12:03

OlliM

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1 Comment

Varun R Over a year ago

Thanks Ollim..yes i will post from next time the code i tried to achieve this. It was good to learn about lodash library. New learning for me :)

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