PHP implementation from the top down to print a binary tree method explained

This article mainly introduces the PHP implementation from the top down to print binary tree, involving PHP two cross-tree traversal related operation skills, the need for friends can refer to the following

The example in this paper describes how PHP implements a binary tree printing from top to bottom. Share to everyone for your reference, as follows:

Problem

Each node of the two-fork tree is printed from top to bottom, and the same-level node prints from left to right.

Solution Ideas

Each layer of the tree is printed from left to right, so it is necessary to save the tree of the nodes, because first-out, so use the queue.

Implementation code

/*class treenode{  var $val;  var $left = NULL;  var $right = NULL;  function __construct ($val) {    $this->val = $val;  }} */function Printfromtoptobottom ($root) {  $queueVal = array ();  $queueNode = Array ();  if ($root = = NULL)    return $queueVal;  Array_push ($queueNode, $root);  while (!empty ($queueNode)) {    $node = Array_shift ($queueNode);    if ($node->left! = NULL)      array_push ($queueNode, $node->left);    if ($node->right! = NULL)      array_push ($queueNode, $node->right);    Array_push ($queueVal, $node->val);  }  return $queueVal;}

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