如何在 STL 中使用reverse_iterator打印单词

How to print words using reverse_iterator in STL

本文关键字：reverse iterator 打印单词 STL 更新时间：2023-10-16

我必须读取两个文本文件，然后将第二个文件中的单词与第一个文件进行比较。然后，我必须显示两个文件中KnownWords相同的单词，其余的不相同单词UnknownWords。下一步是，我必须在DisplayMostFreqKnownWords()中显示最常见的已知单词，在DisplayMostFreqUnknownWords()函数中显示未知单词。我已经成功完成了DisplayMostFreqKnownWords()，到目前为止输出还可以。我将相同的代码从DisplayMostFreqKnownWords()复制到DisplayMostFreqUnknownWords()但在此函数中，它没有在输出中显示任何内容。我不知道出了什么问题。有人能弄清楚这一点吗？

输出为：

Displaying most frequent known words
Word      Count
the        19
a        14
of        11
artificial        11
that        10
to         7
signal         7
and         7
in         6
they         5
Displaying most frequent unknown words
Word      Count

头文件：

typedef map<string, vector<int> > WordMap;
typedef WordMap::iterator WordMapIter;
class WordStats
{
public:
WordStats();
void ReadDictionary();
void DisplayDictionary();
void ReadTxtFile();
void DisplayKnownWordStats();
void DisplayUnknownWordStats();
void DisplayMostFreqKnownWords();
void DisplayMostFreqUnknownWords();
private:
WordMap KnownWords;
WordMap UnknownWords;
WordMapIter Paragraph;
set<string> Dictionary;
char Filename[256];
}

我的程序：

// Displays 10 most frequent words in KnownWords
void WordStats::DisplayMostFreqKnownWords(){
int count;
multimap<int,string > displayFreqWords;// new map with int as key 
(multimap because key could occur more than once)
multimap<int,string >::reverse_iterator rit = displayFreqWords.rbegin();
for (Paragraph = KnownWords.begin();  Paragraph != KnownWords.end(); 
++Paragraph){ // iterate map again
string word = (*Paragraph).first;
int cnt = (*Paragraph).second.size();
displayFreqWords.insert(pair<int,string>(cnt,word));
}
//  multimap<int,string>::iterator rit; // iterator for new map
cout <<"           Word      Countn";
for(; count<=10 && rit!=displayFreqWords.rend(); rit++, ++count){           
string word = (*rit).second;
int cnt = (*rit).first;
cout << setw(15) << word << setw(10) << cnt << endl;
}
}
// Displays 10 most frequent words in UnknownWords
void WordStats::DisplayMostFreqUnknownWords(){
int count;
multimap<int,string > displayFreqUnknownWords;
multimap<int,string >::reverse_iterator rrit = 
displayFreqUnknownWords.rbegin();
for (Paragraph = UnknownWords.begin();  Paragraph != 
UnknownWords.end(); ++Paragraph){ 
string word = (*Paragraph).first;
int cnt = (*Paragraph).second.size();
displayFreqUnknownWords.insert(pair<int,string>(cnt,word));
}
//  multimap<int,string>::iterator rit; // iterator for new map
cout <<"           Word      Countn";
for(; count<=10 && rrit!=displayFreqUnknownWords.rend(); rrit++, ++count){          
string wrd = (*rrit).second;
int ccnt = (*rrit).first;
cout << setw(15) << wrd << setw(10) << ccnt << endl;
}
}

这是一种表达我认为是你的用例的方法。我使用了 c++17 元组扩展。

我用unordered_map来推断哪些单词是已知的或未知的，用两个multimap来确定已知和未知的单词频率。

希望对您有所帮助。

#include <sstream>
#include <tuple>
#include <string>
#include <unordered_map>
#include <algorithm>
#include <iterator>
#include <map>
#include <iostream>
#include <iomanip>
#include <fstream>

// Set this to 1 to run a static test
#define TESTING 0

#if TESTING
using input_type = std::istringstream;
std::tuple<input_type, input_type> open_inputs() {
return {
std::istringstream("the big black cat sat on the grey mat"),
std::istringstream("the gold small cat lay on the purple mat")
};
}
#else
using input_type = std::ifstream;
std::tuple<input_type, input_type> open_inputs() {
return {
std::ifstream("left_file.txt"),
std::ifstream("right_file.txt"),
};
}
#endif
struct Counts {
int left_count = 0, right_count = 0;
int total() const {
return left_count + right_count;
}
bool is_known() const {
return left_count && right_count;
}
};
template<class F>
void for_each_word_in_file(std::istream &is, F f) {
std::for_each(std::istream_iterator<std::string>(is),
std::istream_iterator<std::string>(),
f);
}
int main() {
// open files
auto[left, right] = open_inputs();
auto known_words = std::unordered_map<std::string, Counts>();
// count words in each file
for_each_word_in_file(left, [&known_words](auto &&word) {
++known_words[word].left_count;
});
for_each_word_in_file(right, [&known_words](auto &&word) {
++known_words[word].right_count;
});
// map counts to words, in descending order, allowing multiple entries of the same count
std::multimap<int, std::string, std::greater<>> known_ordered, unknown_ordered;
// iterate all words seen, putting into appropriate map
for (auto&&[word, counts] : known_words) {
(counts.is_known() ? known_ordered : unknown_ordered)
.emplace(counts.total(), word);
}
// emit results
std::cout << "Known words by frequencyn";
for (auto&&[freq, word] : known_ordered) {
std::cout << std::setw(15) << word << " " << freq << 'n';
}
std::cout << "nUmknown words by frequencyn";
for (auto&&[freq, word] : unknown_ordered) {
std::cout << std::setw(15) << word << " " << freq << 'n';
}
}