🍻 Finished ch11

ch11/README.md

@@ -119,3 +119,15 @@ What would happen if a line in that file has a key, one space, and then the end
 we added a file that name "word_transformation_bad.txt" to folder `data`. the file only has a key, one space.
 
 the program of 11.33 don't influenced by that.
+
+## Exercise 11.37:
+>What are the advantages of an unordered container as compared to the ordered version of that container? What are the advantages of the ordered version?
+
+- the advantages of an unordered container:
+    - useful when we have a key type for which there is no obvious ordering relationship among the elements
+    - useful for applications in which the cost of maintaining the elements in order is prohibitive
+- the advantages of the ordered version:
+    - Iterators for the ordered containers access elements in order by key
+    - we can directly define an ordered container that uses a our own class types for its key type.
+
+## [Exercise 11.38](ex11_38.cpp)

ch11/ex11_38.cpp

@@ -0,0 +1,50 @@
+//
+//  ex11_38.cpp
+//  Exercise 11.38
+//
+//  Created by pezy on 12/18/14.
+//  Copyright (c) 2014 pezy. All rights reserved.
+//
+//  Rewrite the word-counting (11.1, p. 421) and word-transformation (11.3.6, p. 440) programs to use an unordered_map.
+
+#include <unordered_map>
+#include <set>
+#include <string>
+#include <iostream>
+#include <fstream>
+#include <sstream>
+
+using std::string;
+
+void wordCounting()
+{
+    std::unordered_map<string, size_t> word_count;
+    for (string word; std::cin >> word; ++word_count[word]);
+    for (const auto &w : word_count)
+        std::cout << w.first << " occurs " << w.second << (w.second > 1 ? "times" : "time") << std::endl;
+}
+
+void wordTransformation()
+{
+    std::ifstream ifs_map("../data/word_transformation.txt"), ifs_content("../data/given_to_transform.txt");
+    if (!ifs_map || !ifs_content) {
+        std::cerr << "can't find the documents." << std::endl;
+        return;
+    }
+
+    std::unordered_map<string, string> trans_map;
+    for (string key, value; ifs_map >> key && getline(ifs_map, value); )
+        if (value.size() > 1) trans_map[key] = value.substr(1).substr(0, value.find_last_not_of(' '));
+
+    for (string text, word; getline(ifs_content, text); std::cout << std::endl)
+        for (std::istringstream iss(text); iss >> word; ) {
+            auto map_it = trans_map.find(word);
+            std::cout << (map_it == trans_map.cend() ? word : map_it->second) << " ";
+        }
+}
+
+int main()
+{
+    //wordCounting();
+    wordTransformation();
+}