JavaScript Permutations using Recursion

Question

I know that there are many solutions on the internet for my specific question, but I have been trying to solve it in a specific way and it doesn't work and I really can't understand what is wrong. In my case I simply want to print the permutations. Here is my code:

a = "abc";


function f7(a, b) {



  //document.write("str: "+a+" b:"+b+"<br>");
  if (b.length == 2) {
    perm = b + a;
    return perm;
  }

  var c = [];
  var str = [];

  for (i = 0; i < a.length; i++) {

    c[i] = b + a.charAt(i);
    str[i] = a.substring(0, i) + a.substring(i + 1);

    document.write("i: " + i + " c[i]: " + c[i] + " str[i]: " + str[i] + "<br>");

    return f7(str[i], c[i]);


  }


  //return {str,c}

}


document.write(f7(a, ""));

//g=f7(a,""); 
//document.write(g.str+"<br>");
//document.write(g.c+"<br>");

The above code doesn't go beyond the first permutation, and I can't understand why. Thanks in advance for any advice

There is no point in a loop with an unconditional return statement inside it, it can never iterate. — Paul
– Paul, Commented Mar 2, 2019 at 6:29

zmag · Accepted Answer · 2019-03-02 06:29:36Z

1

Returning value in the loop causes escaping the loop. You are returning the value in for statement that stops immediately before loop complete.

You can use temporary variable to save value in for loop, and then return it.

a = "abc";


function f7(a, b) {
  //document.write("str: "+a+" b:"+b+"<br>");
  if (b.length == 2) {
    perm = b + a;
    return perm;
  }

  var c = [];
  var str = [];
  var temp = '';

  for (i = 0; i < a.length; i++) {
    c[i] = b + a.charAt(i);
    str[i] = a.substring(0, i) + a.substring(i + 1);

    document.write("i: " + i + " c[i]: " + c[i] + " str[i]: " + str[i] + "<br>");

    temp += f7(str[i], c[i]);
  }

  return temp
}


document.write(f7(a, ""));

//g=f7(a,""); 
//document.write(g.str+"<br>");
//document.write(g.c+"<br>");

answered Mar 2, 2019 at 6:29

zmag

8,27112 gold badges39 silver badges47 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Dan Over a year ago

Hi zmag, thanks for the post. I ran it and now I have 2 specific permutations for my case: abc and acb, but there should be 6 in total (bac bca cab cba) - is it possible to get them all?

zmag Over a year ago

If it's not working properly, maybe its algorithm could be the problem.

Dan Over a year ago

in this link: initjs.org/all-permutations-of-a-set-f1be174c79f8 there is an algorithm that works, and it has the recursion inside the loop - is it because the recursion is being done with a var and not a return?

zmag Over a year ago

I don't think that implementation is the same as yours. in the link, there are loop having inner loop. what did you intend to make your own code?

Dan Over a year ago

Its just that even before looking for the answer I thought I had an idea about how to do it, and I can't figure out why it doesn't work, s it must mean there is something fundamental which I don't understand, so that's why I want to know what it is

Collectives™ on Stack Overflow

JavaScript Permutations using Recursion

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related