判断回文字符串，一句话就够了！

#include <iostream>                                    
   #include <iterator>                                      
   #include <algorithm>                                    
   #include <cctype>                                        
   #include <string>
   using std::string;
   int main()
{  
       //检查一条语句(也可以是很多条语句)是否是回文的
       while(true)
      {
           string sentence;
           std::cout << "Enter a sentence or Ctrl+Z to end: ";
           //etline() 读一条句子到 sentence 中
           std::getline(std::cin, sentence);
           if(std::cin.eof()) break;
           
           string only_letters;
           // copy_if() 将 sentence 中的字母复制到 only_letters
           //只在参数是字母时返回 true，所以其他的任何字符都会被忽略
           std::copy_if(std::begin(sentence), std::end(sentence), std::back_inserter(only_letters),
                  [](char ch) { return std::isalpha(ch); });

           //or_each() 算法会将三个参数指定的函数对象应用到前两个参数定义的序列的元素上      
           //将 only_letters 中的字符全部转换为大写
           std::for_each(std::begin(only_letters), std::end(only_letters),
                    [](char& ch) { ch = toupper(ch); });
         
           string reversed;
           //用 reverse_copy() 算法生成和 only_letters 的内容相反的内容
           std::reverse_copy(std::begin(only_letters), std::end(only_letters), std::back_inserter(reversed));

           //或者以下代替
          // string reversed{only_letters};
          // std::reverse(std::begin(reversed), std::end(reversed));

           //比较 only_letters 和 reversed 来判断输入的语句是否为回文。
           std::cout << '"' << sentence << '"'<< (only_letters == reversed ? " is" : " is not") << " a palindrome." << std::endl;
      }
  }

    #include <iostream>                                    
    #include <vector>                                      
    #include <algorithm>                                    
    #include <string>                                        
    #include <iterator>  
    #include <string>
    #include <deque>
using namespace std;
  
  using std::string;

  int main()
  {
    std::vector<string> names {"A1","Beth", "Carol", "Dan", "Eve","Fred","George" ,"Harry", "Iain", "Joe"};
    std::vector<string> more_names {"Janet", "John"};
    //从 names 的第二个元素开始复制 3 个元素到关联容器 more_names 中
    std::copy_n(std::begin(names)+1, 3, std::inserter(more_names, std::begin(more_names)));
    
    //输出 more_names 中除了最后一个元素之外的全部元素
    std::copy_n(std::begin(more_names), more_names.size()-1,std::ostream_iterator<string> {std::cout, " "});
    cout<<endl;

    //copy_if
    size_t max_length{4};
    //复制 names 中的 4 个字符串或更少
    std::copy_if(std::begin(names), std::end(names), std::inserter(more_names, std::begin(more_names)),
         [max_length](const string& s) { return s.length() <= max_length;});
    std::copy(std::begin(more_names), std::end(more_names), std::ostream_iterator <string>{std::cout, " "});
    std::cout << std::endl;

    //copy_if() 的目的容器也可以是一个流迭代器
    // names 容器中包含的含有 4 个以上字符的名称写到标准输出流中
   std::copy_if(std::begin(names), std::end(names), std::ostream_iterator< string> {std::cout," "},
                 [max_length](const string& s) { return s.length() > max_length; });
   std::cout << std::endl;


   //只有当从标准输入流读取的姓名的长度小于或等于 4 个字符时，copy_if() 算法才会复制它们
    std::cout << "Enter names of less than 5 letters. Enter Ctrl+Z on a separate line to end:\n";
    std::copy_if(std::istream_iterator<string>{std::cin},std::istream_iterator<string>{},
                std::inserter(names, std::begin (names)),
                        [max_length](const string& s) { return s.length() <= max_length; });
    std::copy(std::begin(names), std::end(names), std::ostream_iterator <string>{std::cout," "});
    std::cout << std::endl;


    //copy_backward
    //将原有的元素复制到向右的两个位置，保持前两个元素不变
     std::deque<string> song{ "jingle", "bells","jingle", "all", "the", "way"};
    song.resize(song.size()+2);
    std::copy_backward(std::begin(song), std::begin(song)+6, std::end(song));
    std::copy(std::begin(song), std::end(song), std::ostream_iterator <string> {std::cout, " "});
    std::cout << std::endl;

  }

   #include <iostream>                                    
    #include <iterator>                                      
    #include <algorithm>                                    
    #include <cctype>                                        
    #include <string>
    using std::string;
    int main()
    {  

        //通过覆盖来消除 words 中的连续元素
        std::vector<string> words {"one", "two", "two", "three", "two", "two", "two"};
        auto end_iter = std::unique(std::begin(words), std::end(words));
        // erase() 会移除新的结束迭代器之后的所有元素，因此 end(words) 会返回 end_iter
        words.erase(end_iter, std::end(words));
        std::copy (std::begin (words) , std::end (words) , std::ostream_iterator<string> {std::cout, " "});
        std::cout << std::endl;

        // unique() 会移除字符串 text 中的连续重复的空格
        //在没有重复元素的新字符串之后的所有字符都会被移除。
        string text {"There's   no air in   spaaaaaace!"};
        text.erase(std::unique(std::begin(text), std::end(text),
                [](char ch1, char ch2) { return ch1 = ' '&& ch1 == ch2; }), std::end(text));
        std::cout << text << std::endl; // Outputs: There's no air in spaaaaaace!
    }