Sequential linear representation example of php implementation

In this paper, an example is given to describe the sequential linear table implemented by php. Share it for your reference, as follows:

<?php
/*
 *  Linear sequence table  , It is stored in memory in sequence , Except for the beginning and the end 11 Connected (1 Is generally used 1 Formal representation of dimensional array )
 *
 * GetElem:  Returns the first in the linear table $index Data elements 
 * ListLength:  Returns the length of the linear table 
 * LocateElem:  Returns the position of a given data element in the linear table 
 * PriorElem:  Returns the preceding of the specified element 1 Elements 
 * NextElem:  Returns the after of the specified element 1 Elements 
 * ListInsert:  In the first index Insert an element at the position of elem
 * ListDelete:  Delete the index Element of location elem
 */
class Sequence {
  public $seqArr;
  public $length;
  public function __construct($arr) {
    $this->seqArr = $arr;
    $this->length = count($arr);
  }
  /*
   *  Returns the first in the linear table $index Data elements 
   */
  public function GetElem($index) {
    if (($this->length) == 0 || $index < 0 || ($index > $this->length)) {
      return "Error";
    }
    return $this->seqArr[$index - 1];
  }
  /*
   *  Returns the length of the linear table 
   *
   */
  public function ListLength() {
    return $this->length;
  }
  /*
   *  Returns the position of a given data element in the linear table 
   */
  public function LocateElem($elem) {
    for ($i = 0; $i < ($this->length); $i++) {
      if (($this->seqArr[$i]) == $elem) {
        return $i + 1;
      }
    }
  }
  /*
   * PriorElem:  Returns the preceding of the specified element 1 Elements 
   */
  public function PriorElem($elem) {
    for ($i = 0; $i < ($this->length); $i++) {
      if (($this->seqArr[$i]) == $elem) {
        if ($i == 0) {
          return "Error (is null) ";
        } else {
          return $this->seqArr[$i - 1];
        }
      }
    }
  }
  /*
   * NextElem:  Returns the after of the specified element 1 Elements 
   */
  public function NextElem($elem) {
    for ($i = 0; $i < ($this->length); $i++) {
      if (($this->seqArr[$i]) == $elem) {
        return $this->seqArr[$i + 1];
      }
    }
  }
  /*
   * ListInsert:  In the first index Insert an element at the position of elem
   */
  public function ListInsert($index, $elem) {
    if (($this->length) == 0 || $index < 0 || $index > ($this->length)) {
      return "Error";
    }
    for ($i = $index; $i < ($this->length); $i++) {
      $this->seqArr[$i + 1] = $this->seqArr[$i];
    }
    $this->seqArr[$index] = $elem;
    $this->length = $this->length + 1;
    return $this->seqArr;
  }
  /*
   * ListDelete:  Delete the index Element of location 
   */
  public function ListDelete($index) {
    if (($this->length) == 0 || $index < 0 || $index > ($this->length - 1)) {
      return "Error";
    }
    unset($this->seqArr[$index]);
    $this->length--;
    return $this->seqArr;
  }
}
?>

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