PHP printing binary tree from top to bottom implementation method

This article mainly introduces the method of printing a binary tree from top to bottom in PHP, involving operating techniques related to PHP binary tree traversal. Friends who need it can refer to it. I hope it can help everyone.

Question

Print each node of the binary tree from top to bottom, and print nodes at the same level 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;
}

Related recommendations:

PHP sequence Implementation method of printing binary tree

PHP implements pre-order, in-order and post-order traversal binary tree operation examples

How PHP implements judging whether a binary tree is symmetrical

The above is the detailed content of PHP printing binary tree from top to bottom implementation method. For more information, please follow other related articles on the PHP Chinese website!