Traversing B-Tree Structure Algorithm - php

Question

I'm having a hard time trying to write a traversing function that outputs a child-node's parent-nodes.
Take a look at the example b-tree
Here is the sample dataset I'm using:
$nodes = array(
array('f','b'),
array('f','g'),
array('b','a'),
array('b','d'),
array('g','i'),
array('d','c'),
array('d','e'),
array('i','h')
);
I'm trying to output a results array that contains all child node arrays which contain parent associations.
Example Outputs:
node(d)'s parents are (b,f)
node(c)'s parents are (d,b,f)
node(h)'s parents are (i,g,f)
I can't figure out how to traverse past the direct parent node.
foreach($nodes as $node){
//CHECK IF NODE EXISTS
if(array_key_exists($node[1],$results)){
//DO NOTHING
array_push($results[$node[1]],$node[0]);
}
else{
//CREATE NEW CHILD ARRAY
$results[$node[1]] = [];
//PUSH PARENT INTO CHILD ARRAY
array_push($results[$node[1]],$node[0]);
}
}
foreach($results as $k => $v){
echo "child[$k] parents(" . implode($v,', ').")" ;
echo "</br>";
}
Question: How can I achieve this output in the most efficient manor?

Answer 1

The best way to deal with such cases is to use recursive functions.
echo findParents('h',$nodes);
function findParents($find,$btree){
$parents;
foreach($btree as $node){
if($node[1]===$find){
$parents .=$find.',';
return $parents .= findParents($node[0], $btree);
}
}
return $find;
}
Check the live code here: https://www.tehplayground.com/ElTdtP61DwFT1qIc
The only drawback is that it would return the original node in the return list. But I think you can live with that.
I think the better representation of the tree would be:
$nodes = array(
'f'=>array('d','g'),
'b'=>array('a','d'),
'g'=>array('i'),
'd'=>array('c','e'),
'i'=>array('h')
);
But that would need slight modification to the above code.
To get an array as the response:
function findParentsArray($find,$btree){
$parentsArray = explode(',',findParents($find,$btree));
array_shift($parentsArray);
return $parentsArray;
}
It should be possible to have that done directly in findParents() but I don't have time to look into it now.