综述
富文本在我们平常的项目中应用已经很广泛了，并逐渐发展成了一个行业。最近在项目中遇到需要提取富文本字符串中的文本内容，本篇博文就是记述如何重富文本字符串中提取出文本内容，欢迎大家相互学习。
富文本字符样例
<h1 style="-webkit-tap-highlight-color: transparent; box-sizing: border-box; font-size: 24px; margin: 36px 0px 22px; padding: 0px; line-height: 32px; color: rgb(34, 34, 34); font-family: "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);">
一、算法最最基础
</h1>
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1、时间复杂度
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2、空间复杂度
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一般最先接触的就是时间复杂度和空间复杂度的学习了，这两个概念以及如何计算，是必须学的，也是必须最先学的，主要有最大复杂度、平均复杂度等，直接通过博客搜索学习即可。
</p>
<h1 style="-webkit-tap-highlight-color: transparent; box-sizing: border-box; font-size: 24px; margin: 36px 0px 22px; padding: 0px; line-height: 32px; color: rgb(34, 34, 34); font-family: "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);">
二、基础数据结构
</h1>
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1、线性表
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列表（必学）
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链表（必学）
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跳跃表（知道原理，应用，最后自己实现一遍）
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并查集（建议结合刷题学习）
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不用说，链表、列表必须，不过重点是链表。
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2、栈与队列
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栈（必学）
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队列（必学）
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优先队列、堆（必学）
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多级反馈队列（原理与应用）
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特别是优先队列，再刷题的时候，还是经常用到的，队列与栈，是最基本的数据结构，必学。可以通过博客来学习。相关文章：
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三分钟基础知识：什么是栈？
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二叉堆是什么鬼？
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【算法与数据结构】堆排序是什么鬼？
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3、哈希表（必学）
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碰撞解决方法：开放定址法、链地址法、再次哈希法、建立公共溢出区（必学）
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布隆过滤器（原理与应用）
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哈希表相关的，推荐通过博客来学习，推荐文章：
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Hash冲突之开放地址法
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4、树
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二叉树：各种遍历（递归与非递归）（必学）
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哈夫曼树与编码（原理与应用）
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AVL树（必学）
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B 树与 B+ 树（原理与应用）
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前缀树（原理与应用）
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红黑树（原理与应用）
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线段树（原理与应用）
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5、数组
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树状数组
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矩阵（必学）
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树状数组其实我也没学过
</p>
处理富文本字符串内容
1. 首先通过php的htmlspecialchars_decode()函数把预定义的 HTML 实体 "<"（小于）和 ">"（大于）转换为字符；
2. 其次通过str_replace() 将HTML中的空格换成空；
3. 最后再通过strip_tags()函数剥去字符串中的 HTML、XML 以及 PHP 的标签，即可得到想要的txt纯文本内容。
代码实现
//从数据库获取富文本string
$string = $data["content"];
//把一些预定义的 HTML 实体转换为字符
$html_string = htmlspecialchars_decode($string);
//将空格替换成空
$content = str_replace(" ", "", $html_string);
//函数剥去字符串中的 HTML、XML 以及 PHP 的标签,获取纯文本内容
$contents = strip_tags($content);
//返回字符串中的前80字符串长度的字符
$text = mb_substr($contents, 0, 80, "utf-8");
//打印输出
var_dump($text);
exit;
