My first permutation lesson - what is this code missing?

Question

Translated (apparently wrongly) from a C++ book. If I can get it to work, then I can start trying to understand it.

function recPermute(soFar, rest)
{
    if (rest==="")
    {
        console.log(soFar);    
    }
    else
    {
        for(i=0; i<rest.length; i++) // <<< error was in not declaring the "i"
        {
            var next = soFar + rest[i];
            var remaining = rest.substr(0,i) + rest.substr(i+1);
            recPermute(next, remaining);
        }
    }
}   


function listPerm(s)
{
    recPermute("",s);
}

listPerm("kitcap")

What's wrong with your code? Is there an error, or is it not doing what you think it's doing? — Grim..., Aug 22 '13 at 20:17
Yeah...when you post questions here, you can't just post code and be like HAVE FUN FINDING THE PROBLEM!M!MM! You actually have to say what the problem is. If you don't know, you need to try and describe what's happening as best you can. — temporary_user_name, Aug 22 '13 at 20:18
Could be wrong since I don't really know C++, but it looks like in your JavaScript code you're recursively calling your recPermute function, but in your C++ code you're not. — callmehiphop, Aug 22 '13 at 20:18
You seem to have an eternal loop as callmehiphop pointed out. — Jack M., Aug 22 '13 at 20:19

score 1 · Answer 1 · answered Aug 22 '13 at 20:20

1

for JavaScript, use charAt(), instead of using array like acessing.

var next = soFar + rest.charAt(i);

answered Aug 22 '13 at 20:20

Shamim Hafiz - MSFT

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What's the difference between the two? – Joseph Silber Aug 22 '13 at 20:27
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@JosephSilber `.charAt()` has been part of the language longer. Array-like access is [new with ES5](http://es5.github.io/#x15.5.5.2). So, can't be used in older browsers, if they need to be supported. – Jonathan Lonowski Aug 22 '13 at 20:33

score 1 · Accepted Answer · edited May 23 '17 at 12:13

1

You need to declare i so it's scoped to recPermute:

for(var i=0; i<rest.length; i++)

Without the var, it'll be created as a global so each call to recPermute will alter it for any other calls.

edited May 23 '17 at 12:13

Community

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answered Aug 22 '13 at 20:21

Jonathan Lonowski

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score 0 · Answer 3 · answered Aug 22 '13 at 20:21

0

One thing that could be an issue is you are using effectively the same i for each call to the function. You need to declare a local i or it will be declared in the global scope.

for(var i = 0; ....

answered Aug 22 '13 at 20:21

doogle

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My first permutation lesson - what is this code missing?

3 Answers3