Generate all combinations of characters in javascript

Question

I'm trying to output all the possible combinations of 4 character strings using uppercase letters.

function makeid(length) {
   var result           = '';
   var characters       = 'ABCDEFGHIJKLMNPRSTUVWXYZ';
   var charactersLength = characters.length;
   for ( var i = 0; i < length; i++ ) {
      result += characters.charAt(Math.floor(Math.random() * charactersLength));
   }
   return result;
}

function getcodes(){
 var newcode =makeid(4);
 if (codes.includes(newcode)){
    getcodes();   
 }
 else 
 {
    codes.push(newcode) 
    document.getElementById("demo").innerHTML += newcode + "<br>";
    getcodes();   
  }
} 
getcodes() 
console.log(codes.length)

The problem, of course, is that this loops forever. I'm not sure how to stop the loop when all the codes have been generated. How can I stop this after all combinations have been created?

The use case is that we're trying to generate unique URLs that will be something like example.com/CODES-HERE The codes generated with this script will be used for the CODES-HERE part.

Can you at least leave a small note, as to why you intend to solve a combinatorical problem with random? — ASDFGerte
– ASDFGerte, Commented Mar 17, 2020 at 17:06
@ASDFGerte Just added. The use case is that we're trying to generate unique URLs that will be something like example.com/CODES-HERE The codes generated with this script will be used for the CODES-HERE part. — jonmrich
– jonmrich, Commented Mar 17, 2020 at 17:11
If your intentions are simply to generate the combinations, then don't use random, search on SO (or other sites) for one of the 832475342 solutions for "generate all combinations", and use that? — ASDFGerte
– ASDFGerte, Commented Mar 17, 2020 at 17:12
Why would you use random numbers? It literally is nested loops. — epascarello
– epascarello, Commented Mar 17, 2020 at 17:13

pank · Accepted Answer · 2020-03-18 08:35:38Z

// there are 26! / (4! * 22!) = 14950 combinations possible. it takes a lot of time to get all those by trying random characters 
const chrs = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
// function that returns the cartesian product of two arrays, excluding combinations with repeating characters or 
// not in alphabetic order (because ACB is the same combination with ABC)
const cartesian = (arr1, arr2) => arr1.flatMap(x => arr2.filter(v => x < v[0]).map(y => x + y));
const combs = (ra, n) => [...Array(n - 2)].reduce(a => cartesian(ra, a), cartesian(ra, ra));
const str = combs([...chrs], 4).reduce((a, v) => a + v + '<br>', '');
document.getElementById("demo").innerHTML = str;
// if you want to allow combinations with repeating characters or not in alphabetic order
// remove the filter from cartesian
// but there are 26 ** 4 = 456976 possible outcomes then, so it'll take some time to print them all

Collectives™ on Stack Overflow

Generate all combinations of characters in javascript

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related