#!/usr/bin/env php
<?php
class Node {
  public $data;
  public $next;
}

class LinkedList {
  public  $head;

  public function __construct(){
    $this->head = null;
  }

  public function push_back($newElement) {
    $newNode = new Node();
    $newNode->data = $newElement;
    $newNode->next = null;
    if($this->head == null) {
      $this->head = $newNode;
    } else {
      $temp = new Node();
      $temp = $this->head;
      while($temp->next != null) {
        $temp = $temp->next;
      }
      $temp->next = $newNode;
    }
  }

  public function push_at($newElement, $position) {
    $newNode = new Node();
    $newNode->data = $newElement;
    $newNode->next = null;

    if($position < 1) {
      echo "\nposition should be >= 1.";
    } else if ($position == 1) {
      $newNode->next = $this->head;
      $this->head = $newNode;
    } else {

      $temp = new Node();
      $temp = $this->head;
      for($i = 1; $i < $position-1; $i++) {
        if($temp != null) {
          $temp = $temp->next;
        }
      }

      if($temp != null) {
        $newNode->next = $temp->next;
        $temp->next = $newNode;
      } else {
        echo "\nThe previous node is null.";
      }
    }
  }

  public function PrintList() {
    $temp = new Node();
    $temp = $this->head;
    if($temp != null) {
      echo "The list contains: ";
      while($temp != null) {
        echo $temp->data." ";
        $temp = $temp->next;
      }
      echo "\n";
    } else {
      echo "The list is empty.\n";
    }
  }
};

$MyList = new LinkedList();

$MyList->push_back(10);
$MyList->push_back(20);
$MyList->push_back(30);
$MyList->PrintList();

$MyList->push_at(100, 2);
$MyList->PrintList();

$MyList->push_at(200, 1);
$MyList->PrintList();
?>
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