谈c++ pb_ds库（一）rope大法好
(转载)原文链接 https://www.cnblogs.com/keshuqi/p/6257642.html
参考资料
1）官方说明
支持
sorry，cena不支持rope
声明
1）头文件
#include<ext/rope>
2)调用命名空间
using namespace __gnu_cxx;
底层原理
查了资料，大概可以称作可持久化平衡树，因为rope适用于大量、冗长的串操作，而不适合单个字符操作官方说明如下：
Though ropes can be treated as Containers of characters, and are almost Sequences, this is rarely the most efficient way to accomplish a task. Replacing an individual character in a rope is slow: each character replacement essentially consists of two substring operations followed by two concatenation operations. Ropes primarily target a more functional programming style.Inserting a character in the middle of a 10 megabyte rope should take on the order of 10s of microseconds, even if a copy of the original is kept, e.g. as part of an edit history.It is possible to view a function producing characters as a rope. Thus a piece of a rope may be a 100MByte file, which is read only when that section of the string is examined. Concatenating a string to the end of such a file does not involve reading the file. (Currently the implementation of this facility is incomplete.)
另，根据网上资料，rope本质是封装好的类似块状链表的东东，有人说是logn的，但也有说是n^0.5的。rope不支持一切数值操作，如第k大
小知识
先介绍几个可能使用到的函数
1）append()
string &append(const string &s,int pos,int n);//把字符串s中从pos开始的n个字符连接到当前字符串的结尾
或
a.append(b);
2）substr()
s.substr(0,5);//获得字符串s中从第零位开始长度为5的字符串（默认时长度为刚好开始位置到结尾）
定义/声明
rope<char> str;
also
<crope>r="abcdefg"
具体内容
总的来说，
1）运算符：rope支持operator += -= + - < ==
2）输入输出：可以用<<运算符由输入输出流读入或输出。
3）长度/大小：调用length()，size()都可以哦
4）插入/添加等：
push_back(x);//在末尾添加x
insert(pos,x);//在pos插入x，自然支持整个char数组的一次插入
erase(pos,x);//从pos开始删除x个
copy(pos,len,x);//从pos开始到pos+len为止用x代替
replace(pos,x);//从pos开始换成x
substr(pos,x);//提取pos开始x个
at(x)/[x];//访问第x个元素
访问
1）迭代器：不说，在竞赛是超时大忌
2）单点访问，直接用数组形式调用下标即可