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  1. #include <iostream>
  2. #include <iterator>
  3. #include <fstream>
  4. #include <string>
  5. #include <boost/date_time/gregorian/gregorian.hpp>
  6.  
  7. struct Log
  8. {
  9.     typedef boost::gregorian::date Date;
  10.     Date date;
  11.     int info;
  12. };
  13.  
  14. std::ostream& operator <<(std::ostream& os, const Log& l)
  15. {
  16.     return os << l.date << " " << l.info;
  17. }
  18.  
  19. std::istream& operator >>(std::istream& is, Log& l)
  20. {
  21.     return is >> l.date >> l.info;
  22. }
  23.  
  24. Log LowerBound(std::istream& os, Log::Date d)
  25. {
  26.     using namespace std;
  27.     os.seekg(0, std::ios::end);
  28.     streamoff length = os.tellg();
  29.     streampos current = 0;
  30.     Log l;
  31.     for(; length > 0;)
  32.     {
  33.         streamoff half = length / 2;
  34.         streampos mid = current + half;
  35.         os.seekg(mid);
  36.  
  37.         string line;
  38.         getline(os, line);
  39.  
  40.         if (!(os >> l.date >> l.info))
  41.             throw std::runtime_error("bad log format");
  42.         if (l.date < d)
  43.         {
  44.             mid += 1;
  45.             current = mid;
  46.             length = length - half + 1;
  47.         }
  48.         else
  49.             length = half;
  50.     }
  51.     return l;
  52. }
  53.  
  54. template<typename OutIter>
  55. void ReadLogsInRange(
  56.     std::istream& logStream, Log::Date from, Log::Date to, OutIter out)
  57. {
  58.     using namespace std;
  59.  
  60.     Log l = LowerBound(logStream, from);
  61.     *out++ = l;
  62.     // Upper Bound
  63.     while(logStream >> l && l.date < to)
  64.         *out++ = l;
  65. }
  66.  
  67.  
  68. int main()
  69. {
  70.     using namespace boost::gregorian;
  71.  
  72.     // Create log
  73.     Log l;
  74.     l.date = Log::Date(2011, Sep, 1);
  75.     l.info = 1;
  76.  
  77.     std::stringstream log;
  78.     for(int i = 0; i < 1000; ++i)
  79.     {
  80.         log << l << std::endl;
  81.         l.date += days(1);
  82.         ++l.info;
  83.     }
  84.  
  85.     // Read the log
  86.     std::vector<Log> range;
  87.     ReadLogsInRange(log, 
  88.         date(2011, Sep, 9), date(2011, Sep, 12), 
  89.         std::back_inserter(range));
  90.  
  91.     std::copy(range.begin(), range.end(), 
  92.         std::ostream_iterator<Log>(std::cout, "\n"));
  93. }
Success #stdin #stdout 0s 2932KB
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2011-Sep-09 9
2011-Sep-10 10
2011-Sep-11 11
https://ideone.com/CvIYm
language:
C++ (gcc 8.3)
created:
12 years ago
visibility:
public

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