### Find time from time ranges (including overlapping ranges)

This is a very simple problem. In this trying to find a given time from ranges of times. So, I have a collection which stores different time ranges (including overlapping time ranges). The job is to find or search if a time provided by user exists in time ranges collection.

Example: Let's assume I have following collections of time ranges:

1. 07:00 - 09:00
2. 13:45 - 15:15
3. 16:25 - 18:10
4. 08:30 - 10:00

Now, need to find if time 09:30 is present in that collection or not. If it finds it shall print true, otherwise false. Similarly it can be use to check other times too.

Solution: To store time ranges, what I did is converted start and end time to decimal numbers respectively and stored them in STL's set (multiset) used to address overlapping ranges. As we know that set data structure in STL is a tree (Red Black Tree / Balanced Binary tree).

Time Complexity:
1. set::insert - If N elements are inserted, Nlog(size+N). Implementations may optimize if the range is already sorted. (Reference: set::insert)
2. set::find - Logarithmic in size (size of the set). (Reference: set::find)

The set templates signature in STL is like below:
```template < class T,                        // set::key_type/value_type
class Compare = less<T>,        // set::key_compare/value_compare
class Alloc = allocator<T>      // set::allocator_type
> class set;```

It has a template argument key_compare. So, we need to provide a compare function which will do comparison with respect to ranges and sort (using strict weak ordering) while storing ranges as well as help us to find if a time is part of any range(s) stored in the set.

To solve this I have followed a structure like header only library and used it in main.cpp. A namespace config has been used to control if seconds need to be processed to generate decimal or not. To do so used inline global variable in config namespace which helped to decouple configuration from API to find date in ranges.

Solution Code:
// mylib.h
#ifndef MYLIB
#define MYLIB

#include <iostream>
#include <iomanip>
#include <set>
#include <sstream>
#include <string>

using std::tm;
using std::istringstream;
using std::string;
using std::multiset;
using std::pair;

namespace my_lib
{
namespace config
{
inline bool compute_seconds = false;
}

typedef pair<double, double> timeranges;
struct timeRangeCompare
{
bool operator()(const timeranges& lvalue, const timeranges& rvalue) const
{
return lvalue.second < rvalue.first;
}
};

bool isInRange(const multiset<timeranges, timeRangeCompare>& iRanges,
double value)
{
return iRanges.find(timeranges(value, value)) != iRanges.end();
}

double convert_StringTime(string& s)
{
std::tm tm;
istringstream ss(s);
double fNumber = 0.;

if (!config::compute_seconds)
{
ss >> std::get_time(&tm, "%H:%M");
fNumber = tm.tm_hour + (tm.tm_min / 60.0);
}
else
{
ss >> std::get_time(&tm, "%T");
fNumber = tm.tm_hour + (tm.tm_min / 60.0) + (tm.tm_sec / 3600.0);
/* The construct (tm.tm_min / 60.0) may results in warning
'The left operand of '/' is a garbage value' by clang-tidy tool.
In that case we can replace "%T" format to "%H:%M:%S"*/
}
return fNumber;
}
}

#endif

// main.cpp
#include "mylib.h"

using std::cout;
using std::string;
using std::boolalpha;

int main()
{
// This part deals with time ranges including overlapping
multiset<my_lib::timeranges, my_lib::timeRangeCompare> rangesObj;

// Time range: 1
string sStartTime{"10:15"};
string sEndTime{ "12:15" };
double fStartTime = my_lib::convert_StringTime(sStartTime);
double fEndTime = my_lib::convert_StringTime(sEndTime);
rangesObj.insert(my_lib::timeranges(fStartTime, fEndTime));

// Time range: 2
sStartTime = "14:30";
sEndTime = "15:15";
fStartTime = my_lib::convert_StringTime(sStartTime);
fEndTime = my_lib::convert_StringTime(sEndTime);
rangesObj.insert(my_lib::timeranges(fStartTime, fEndTime));

// Time range: 3.
// This is overlapping range with Time range 1(above)
my_lib::config::compute_seconds = true; // Now seconds will be used to compute number

sStartTime = "11:30:45";
sEndTime = "12:40:23";
fStartTime = my_lib::convert_StringTime(sStartTime);
fEndTime = my_lib::convert_StringTime(sEndTime);
rangesObj.insert(my_lib::timeranges(fStartTime, fEndTime));

// Now check a time if it's within a range
// Should display true as it's already in range
string sTimeToCheck{ "12:10:00" };
double dToCheck = my_lib::convert_StringTime(sTimeToCheck);
cout << boolalpha << my_lib::isInRange(rangesObj, dToCheck) << "\n";

// This one isn't in time slots hence must return false;
sTimeToCheck = "16:30:00";
dToCheck = my_lib::convert_StringTime(sTimeToCheck);
cout << boolalpha << my_lib::isInRange(rangesObj, dToCheck) << "\n";

return 0;
}

*** VS-2019 is used with flag set to /std:c++17.

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