How to store a binary tree as one-dimensional array? - php

Question

How to construct data into a binary tree sort to output a one-dimensional array?
Now that I have constructed the data into a binary tree, how can I recursively solve the binary tree as a one-dimensional array with the following code and data:
Data
$nodes = array(8,3,10,1,6,14,4,7,13);
Construct a binary tree code
function insertNode($node,$newNode){
//var_dump($node);
//var_dump($newNode);
//exit;
if ($node['key'] < $newNode['key']){
if (empty($node['right'])){
$node['right'] = $newNode;
}else{
$node['right'] = insertNode($node['right'],$newNode);
}
}elseif ($node['key'] > $newNode['key']){
if (empty($node['left'])){
$node['left'] = $newNode;
}else{
$node['left'] = insertNode($node['left'],$newNode);
}
}
return $node;
}
function tree($nodes)
{
$node = [
'key' => '',
'left' => '',
'right' => ''
];
$newNode = [
'key' => '',
'left' => '',
'right'=> ''
];
foreach ($nodes as $key => $value){
//insert($value,$key);
if($key == 0)
{
$node['key'] = $value;
continue;
}
$newNode['key'] = $value;
//Constructing a binary tree
$node = insertNode($node,$newNode);
}
//Recursive solution
$node = midSortNode($node);
return $node;
}
var_dump(tree($nodes));
The following is my constructed binary tree
array (size=3)
'key' => int 8
'left' =>
array (size=3)
'key' => int 3
'left' =>
array (size=3)
'key' => int 1
'left' => string '' (length=0)
'right' => string '' (length=0)
'right' =>
array (size=3)
'key' => int 6
'left' =>
array (size=3)
...
'right' =>
array (size=3)
...
'right' =>
array (size=3)
'key' => int 10
'left' => string '' (length=0)
'right' =>
array (size=3)
'key' => int 14
'left' =>
array (size=3)
...
'right' => string '' (length=0)
I need to recursively classify the binary tree into a well-ordered one-dimensional array.
My code is as follows
function midSortNode($node){
$sortArr = [];
if (!empty($node)){
$sortArr[] = midSortNode($node['left']);
//$sortArr['left'] = midSortNode($node['left']);
array_push($sortArr,$node['key']);
$sortArr[] = midSortNode($node['right']);
//$sortArr['right'] = midSortNode($node['right']);
}
return $sortArr;
}
var_dump(midSortNode($node));
Here is the result, but not what I want
0 =>
array (size=3)
0 =>
array (size=3)
0 =>
array (size=0)
...
1 => int 1
2 =>
array (size=0)
...
1 => int 3
2 =>
array (size=3)
0 =>
array (size=3)
...
1 => int 6
2 =>
array (size=3)
...
1 => int 8
2 =>
array (size=3)
0 =>
array (size=0)
empty
1 => int 10
2 =>
array (size=3)
0 =>
array (size=3)
...
1 => int 14
2 =>
array (size=0)
...
How to solve the binary tree as follows
array (size=9)
0 => int 1
1 => int 3
2 => int 4
3 => int 6
4 => int 7
5 => int 8
6 => int 10
7 => int 13
8 => int 14

Answer 1

I'm assuming that your happy with the steps so far, so the main code as it is isn't changed. All I think you need to do is to extract the data from the final tree into a 1 dimensional array. As the items are all leaf nodes and in order, you can just use array_walk_recursive() to go over all of the nodes and add them to a new array...
$tree = tree($nodes);
array_walk_recursive( $tree,
function ($data) use (&$output) { $output[] = $data;} );
print_r($output);
gives...
Array
(
[0] => 1
[1] => 3
[2] => 4
[3] => 6
[4] => 7
[5] => 8
[6] => 10
[7] => 13
[8] => 14
)
Edit:
To update the existing code to do this, you can change the midSortNode() to pass around the list of outputs and only add in the current node...
function midSortNode($node, $sortArr = []){
if (!empty($node)){
$sortArr = midSortNode($node['left'], $sortArr);
$sortArr[] = $node['key'];
$sortArr = midSortNode($node['right'], $sortArr);
}
return $sortArr;
}