C++primer 11.3.7节练习
练习11.37
在关键字类型的元素没有明显的序关系的情况下，无序容器是非常有用的，在某些应用中，维护元素的序代价非常高昂，此事无序容器也很有用
练习11.38
单词计数程序
1 #include <iostream> 2 #include <fstream> 3 #include <string> 4 #include <sstream> 5 #include <set> 6 #include <map> 7 #include <algorithm> 8 #include <vector> 9 #include <algorithm> 10 #include <iterator> 11 #include <unordered_map> 12 13 using namespace std; 14 15 16 17 int main() 18 { 19 unordered_map<string, size_t> words_count; 20 string word; 21 while (cin >> word) 22 { 23 ++words_count[word]; 24 } 25 26 for (auto c : words_count) 27 { 28 cout << c.first << " occurs " << c.second << endl; 29 } 30 system("pause"); 31 return 0; 32 }
单次转换程序
1 #include <iostream> 2 #include <fstream> 3 #include <string> 4 #include <sstream> 5 #include <set> 6 #include <map> 7 #include <algorithm> 8 #include <vector> 9 #include <algorithm> 10 #include <iterator> 11 #include <unordered_map> 12 13 using namespace std; 14 15 void word_transform(ifstream &map_file, ifstream &input); 16 unordered_map<string, string> buildMap(ifstream &map_file); 17 const string &transform(const string &s, const unordered_map<string, string> &m); 18 19 int main() 20 { 21 ifstream test1("test1.txt"); 22 ifstream test2("test2.txt"); 23 word_transform(test1, test2); 24 system("pause"); 25 return 0; 26 } 27 28 void word_transform(ifstream &map_file, ifstream &input) 29 { 30 auto trans_map = buildMap(map_file); 31 string text; 32 while (getline(input, text)) 33 { 34 istringstream stream(text); 35 string word; 36 bool firstword = true; 37 while (stream >> word) 38 { 39 if (firstword) 40 firstword = false; 41 else 42 cout << " "; 43 cout << transform(word, trans_map); 44 } 45 cout << endl; 46 } 47 } 48 49 unordered_map<string, string> buildMap(ifstream & map_file) //将文件的转换规则放在map内 50 { 51 unordered_map<string, string> tran_map; 52 string key; 53 string value; 54 while (map_file >> key && getline(map_file, value)) 55 { 56 try { 57 if (value.size() > 1) 58 tran_map[key] = value.substr(1); 59 else 60 throw runtime_error("no rule for " + key); 61 } 62 catch (runtime_error error) 63 { 64 cout << error.what() << endl; 65 } 66 } 67 return tran_map; 68 } 69 70 const string & transform(const string & s, const unordered_map<string, string>& m) //将字符串按照规则进行转换 71 { 72 auto map_it = m.find(s); 73 if (map_it != m.cend()) 74 return map_it->second; 75 else 76 return s; 77 // TODO: 在此处插入 return 语句 78 }
