An explanation of how to print a binary tree from top to bottom in PHP

This article mainly introduces the method of printing binary trees from top to bottom in PHP, involving the operation skills related to PHP binary tree traversal. Friends who need it can refer to it

The example of this article tells about the implementation of PHP from top to bottom Method to print binary tree. Share it with everyone for your reference, the details are as follows:

Question

Print each node of the binary tree from top to bottom, nodes at the same level Print from left to right.

Solution

Each layer of trees is printed from left to right, so the left and right subtrees of the node need to be stored, because first in, first out , so use 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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