PHP implements sequential linear table

What is a linear sequence table?

Linear sequence table refers to storage in memory in order, and is connected one by one except the beginning and end (usually expressed in the form of a one-dimensional array).

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The example code is as follows:

<?php
/*
 * GetElem: 返回线性表中第$index个数据元素
 * ListLength: 返回线性表的长度
 * LocateElem: 返回给定的数据元素在线性表中的位置
 * PriorElem: 返回指定元素的前一个元素
 * NextElem: 返回指定元素的后一个元素
 * ListInsert: 在第index的位置插入元素elem
 * ListDelete: 删除第index位置的元素elem
 */
class Sequence {
  public $seqArr;
  public $length;
  public function __construct($arr) {
    $this->seqArr = $arr;
    $this->length = count($arr);
  }
  /*
   * 返回线性表中第$index个数据元素
   */
  public function GetElem($index) {
    if (($this->length) == 0 || $index < 0 || ($index > $this->length)) {
      return "Error";
    }
    return $this->seqArr[$index - 1];
  }
  /*
   * 返回线性表的长度
   *
   */
  public function ListLength() {
    return $this->length;
  }
  /*
   * 返回给定的数据元素在线性表中的位置
   */
  public function LocateElem($elem) {
    for ($i = 0; $i < ($this->length); $i++) {
      if (($this->seqArr[$i]) == $elem) {
        return $i + 1;
      }
    }
  }
  /*
   * PriorElem: 返回指定元素的前一个元素
   */
  public function PriorElem($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: 返回指定元素的后一个元素
   */
  public function NextElem($elem) {
    for ($i = 0; $i < ($this->length); $i++) {
      if (($this->seqArr[$i]) == $elem) {
        return $this->seqArr[$i + 1];
      }
    }
  }
  /*
   * ListInsert: 在第index的位置插入元素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 $this->seqArr;
  }
  /*
   * ListDelete: 删除第index位置的元素
   */
  public function ListDelete($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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