document_distance.cpp

#include <cctype>
#include <chrono>
#include <cmath>
#include <fstream>
#include <iostream>
#include <numeric>
#include <unordered_map>

using namespace std;
using namespace chrono;

const string readFile(const string &name) {
  ifstream fin(name);
  string temp;
  fin.seekg(0, ios::end);
  size_t fileSize = fin.tellg();
  temp.resize(fileSize);
  fin.seekg(0, ios::beg);
  fin.read(&temp[0], fileSize);
  fin.close();
  return temp;
}

const unordered_map<string, int> wordFrequency(const string &str) {
  unordered_map<string, int> wordMap;
  string temp;
  for (int i = 0; i < str.size(); ++i) {
    char c = str[i];
    if (isalnum(c)) {
      if (isupper(c)) {
        temp += string(1, static_cast<char>(tolower(c)));
      } else {
        temp += string(1, c);
      }
    } else {
      if (wordMap.find(temp) == wordMap.end()) {
        wordMap[temp] = 1;
      } else {
        ++wordMap[temp];
      }
      temp = "";
    }

    if (i == str.size() - 1) {
      if (wordMap.find(temp) == wordMap.end()) {
        wordMap[temp] = 1;
      } else {
        ++wordMap[temp];
      }
    }
  }
  return wordMap;
}

double magnitude(const unordered_map<string, int> &m) {
  int sum_of_square_of_terms = 0;
  for (const auto &e : m) {
    sum_of_square_of_terms += pow(e.second, 2);
  }
  return sqrt(sum_of_square_of_terms);
}

double computeAngle(const unordered_map<string, int> &f1,
                    const unordered_map<string, int> &f2) {
  double res = 0;
  for (auto it1 = f1.begin(); it1 != f1.end(); ++it1) {
    string word_from_file1 = it1->first;
    if (f2.find(word_from_file1) != f2.end()) {
      res += it1->second * f2.find(word_from_file1)->second;
    }
  }

  return acos(res / (magnitude(f1) * magnitude(f2)));
}

float compareFile(const string &name1, const string &name2) {
  const string file1Content = readFile(name1);
  const string file2Content = readFile(name2);
  unordered_map<string, int> wordMap_file1 = wordFrequency(file1Content);
  unordered_map<string, int> wordMap_file2 = wordFrequency(file2Content);
  return computeAngle(wordMap_file1, wordMap_file2);
}

int main() {
  auto begin = system_clock::now();
  cout << compareFile("file1.txt", "file2.txt") << '\n';
  auto end = system_clock::now();
  auto elapsed = duration_cast<milliseconds>(end - begin);
  cout << "Time elapsed in (ms): " << elapsed.count() << '\n';
  return 0;
}