綜述
富文本在我們平常的項目中應用已經很廣泛了，並逐漸發展成了一個行業。最近在項目中遇到需要提取富文本字符串中的文本內容，本篇博文就是記述如何重富文本字符串中提取出文本內容，歡迎大家相互學習。
富文本字符樣例
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一、算法最最基礎
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1、時間複雜度
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2、空間複雜度
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一般最先接觸的就是時間複雜度和空間複雜度的學習了，這兩個概念以及如何計算，是必須學的，也是必須最先學的，主要有最大複雜度、平均複雜度等，直接通過博客搜索學習即可。
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二、基礎數據結構
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1、線性表
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列表（必學）
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鏈表（必學）
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跳躍表（知道原理，應用，最後自己實現一遍）
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並查集（建議結合刷題學習）
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不用說，鏈表、列表必須，不過重點是鏈表。
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2、棧與隊列
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棧（必學）
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隊列（必學）
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優先隊列、堆（必學）
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多級反饋隊列（原理與應用）
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特別是優先隊列，再刷題的時候，還是經常用到的，隊列與棧，是最基本的數據結構，必學。可以通過博客來學習。相關文章：
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三分鐘基礎知識：什麼是棧？
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二叉堆是什麼鬼？
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【算法與數據結構】堆排序是什麼鬼？
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3、哈希表（必學）
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碰撞解決方法：開放定址法、鏈地址法、再次哈希法、建立公共溢出區（必學）
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布隆過濾器（原理與應用）
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哈希表相關的，推薦通過博客來學習，推薦文章：
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Hash衝突之開放地址法
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4、樹
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二叉樹：各種遍歷（遞歸與非遞歸）（必學）
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哈夫曼樹與編碼（原理與應用）
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AVL樹（必學）
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B 樹與 B+ 樹（原理與應用）
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前綴樹（原理與應用）
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紅黑樹（原理與應用）
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線段樹（原理與應用）
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5、數組
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樹狀數組
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矩陣（必學）
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樹狀數組其實我也沒學過
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處理富文本字符串內容
1. 首先通過php的htmlspecialchars_decode()函數把預定義的 HTML 實體 "<"（小於）和 ">"（大於）轉換爲字符；
2. 其次通過str_replace() 將HTML中的空格換成空；
3. 最後再通過strip_tags()函數剝去字符串中的 HTML、XML 以及 PHP 的標籤，即可得到想要的txt純文本內容。
代碼實現
//從數據庫獲取富文本string
$string = $data["content"];
//把一些預定義的 HTML 實體轉換爲字符
$html_string = htmlspecialchars_decode($string);
//將空格替換成空
$content = str_replace(" ", "", $html_string);
//函數剝去字符串中的 HTML、XML 以及 PHP 的標籤,獲取純文本內容
$contents = strip_tags($content);
//返回字符串中的前80字符串長度的字符
$text = mb_substr($contents, 0, 80, "utf-8");
//打印輸出
var_dump($text);
exit;
