recursion in JavaScript graph exploring algorithm

Question

I am trying to explore a graph here but I am not sure what is wrong with the explore function. The recursion doesn't seem to be working correctly; while exploring the neighbours of the node 0 it explored 0, 1, 2 and then never returns back to explore 3, 4, 5; why is that so?

explored=[]
//class definition 
function graph(){
    this.graph=new Array();
    this .graph[0] = [1,0,1,1,0,1]
    this .graph[1] = [0,1,1,1,0,0]
    this .graph[2] = [1,1,1,1,0,0]
    this .graph[3] = [1,1,1,1,1,0]
    this .graph[4] = [0,0,0,1,1,0]
    this .graph[5] = [1,0,0,0,0,0]

    this.explore    = explore

}

function explore(node,depth){

    explored[node]=1
    document.write('<br>')
    for(x=0;x<depth;x++)
        document.write('-')
    document.write(node+'<br>')
    neighbours=this.graph[node]

    document.write('exploring '+node +' neighbours' + neighbours +'explored = '+explored)

    for ( i=0;i<neighbours.length;i++){
        document.write('checking'+i+' node is ='+node )
        if(neighbours[i] ==1 && explored[i]!=1)
            this.explore(i,++depth)
    }

}

g = new graph()
g.explore(0,0)

by not using var you've set both x and i as global variables. — generalhenry
– generalhenry, Commented Feb 8, 2011 at 8:49
@generalhenry You should make it an answer, so he can accept it.. if not, I will do it.. mohowhah..mwhahahaha! — Frode
– Frode, Commented Feb 8, 2011 at 9:15

generalhenry · Accepted Answer · 2011-02-08 09:17:31Z

4

by leaving out var you're setting global variables in a recursive function and stepping on your toes, here's the corrected code

function explore(node,depth){

    explored[node]=1
    document.write('<br>')
    for(**var** x=0;x<depth;x++)
        document.write('-')
    document.write(node+'<br>')
    **var** neighbours=this.graph[node]

    document.write('exploring '+node +' neighbours' + neighbours +'explored = '+explored)

    for (**var** i=0;i<neighbours.length;i++){
        document.write('checking'+i+' node is ='+node )
        if(neighbours[i] ==1 && explored[i]!=1)
            this.explore(i,++depth)
    }

}

answered Feb 8, 2011 at 9:17

generalhenry

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Comments

Zachary K · Accepted Answer · 2011-02-08 10:01:32Z

2

The line this.explore(i,++depth) may also be causing you problems, as you are incrementing depth in the current scope as well as passing the incremented value to the recusive call,

better to use

this.explore(i, depth + 1);

When in doubt with javascript it is always good to check the code with jslint.

edited Feb 8, 2011 at 10:01

answered Feb 8, 2011 at 9:24

Zachary K

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1 Comment

Frode Over a year ago

Hmm, wouldn't that be exactly equivalent? While he doesn't use the depth argument for the actual exploration, I think what he actually wants is this.explore(i, depth + 1) though - so that the depth isn't increased in the calling scope, and indentation will remain correct for that depth.

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