Convert function from recursion to iteration

Question

I have this function that I wrote that is abysmally slow since php does not handle recursion well. I am trying to convert it to a while loop, but am having trouble wrapping

Answer 1

I'm not going to convert your code, but you can convert a recusive function into an iterative one by creating a stack:

$stack= array();

And instead of invoking $this->findroute(), push your parameters onto this stack:

$stack[] = array($i, $distanceSoFar + $this->distanceArray[$curLoc][$i], $expectedValue);

Now surround basically everything in your function into a while loop draining the stack after having primed it:

while ($stack) { 
    // Do stuff you already do in your function here

Answer 2

This looks like your trying to find the optimal route for traversal of a series of nodes in a graph.

I'm guessing that you've not studied Computer Science as the "Travelling Salesman" problem is an archetype of Artificial Intelligence. Of course, as such, it has its own Wikipedia page:

http://en.wikipedia.org/wiki/Travelling_salesman_problem

Sorry - but just swapping from a recursive to an iterative function isn't going to make it go any faster ("php does not handle recursion well." - can you provide reference for this assertion). If you need a faster solution then you'll need to look at non-exhaustive/fuzzy methods.

C.

Answer 3

You can convert a recursive function into an iterative function by using a stack to store the current state. Look into array_push() and array_pop().

Answer 4

At a glance I don't think recursion is your problem, yes it's slow in PHP, but It looks like your going over values more than you need to, putting the values in a stack, or several stacks and handling them, may be nice.

custom sort functions have always helped me with problems of this sort.

function sort_by_visited($x,$y)
{
   return ($this->locationsVisited[$x] > $this->locationsVisited[$y]) ? -1 : 1;
}

uasort($locationsVisited,'sort_by_visited');

This will prioritize all not visited locations at the top of the stack.