Great Circle Distance.cpp

#include <bits/stdc++.h> 
using namespace std; 

// Latitude of customer who needs a cab. 
#define lat1d 12.9611159 

// Longitude of customer who needs a cab. 
#define lon1d 77.6362214 

#define pi 3.14159265358979323846 
#define earth_radius 6371.0 

ifstream customer_list ("customers.json"); 
ofstream out ("answer.json"); 

// Function to convert degree to radian. 
double degtorad(double deg) { 
	return ( deg * pi / 180); 
} 

// Function to calculate distance between 2 given locations using Great Circle Distance Formula. 
double distanceEarth(double lat2d, double lon2d) {				 
	double lat1, lon1, lat2, lon2, 
		delta_lon, central_ang; 

	lat1 = degtorad(lat1d); 
	lon1 = degtorad(lon1d); 
	lat2 = degtorad(lat2d); 
	lon2 = degtorad(lon2d); 

	delta_lon = lon2 - lon1; 
	
	// great circle distance formula. 
	central_ang = acos ( sin(lat1) * sin(lat2) + cos(lat1) * cos(lat2) * cos(delta_lon) ); 
	return (earth_radius * central_ang); 
} 

// Structure which contains data and functions for accessing and processing data from the given customers.json file. 
struct json { 
	long long int length, i, j, x, y, m, n, f, fi, id[100000]; 
	char latitude_as_string[1000], longitude_as_string[1000], id_as_string[1000], name[1000]; 
	double lat2d, lon2d; 
	string line; 
	
	void distance_calculator() { 
		if (distanceEarth(lat2d, lon2d) <= 50.0000) { 
			id[i] = atoll(id_as_string); 
			i++; 
			out << "{\"user_id\": " << id[i - 1] << ", \"name\": " << name << "}" << endl; 
		} 
	} 

	// Function to read various attributes  like latitude, longitude, name , id,  etc, from customers.json file. Simplistic approach is used to get JSON attributes. 
	void json_parser() {					 
		if (customer_list.is_open()) { 
			while (getline(customer_list, line)) { 
				f = 0; x = 0; y = 0; fi = 0; m = 0, n = 0; 
				length = line.size(); 

				for (j = 0; j < length; j++) { 
					if (line[j] == '"') 
						f++; 

					else if (line[j] == ':') 
						fi++; 
            
					if (f == 3) { 
						j++; 
						while (line[j] != '"') { 
							latitude_as_string[x] = line[j]; 
							x++; j++; 
						} 
						j--; 
            					latitude_as_string[x] = '\0'; 
					} 
					 
				  else if (f == 13) { 
						j++; 
						while (line[j] != '"') { 
							longitude_as_string[y] = line[j]; 
							y++; j++; 
						} 
						j--;
            					longitude_as_string[y] = '\0'; 
					} 
					 
					if (fi == 2) { 
						j += 2; 
						while (line[j] != ',') { 
							id_as_string[m] = line[j]; 
							m++; j++; 
						} 
						j--; 
            					id_as_string[m] = '\0'; 
						fi++; 
					} 
					
				  else if (fi == 4) { 
						j += 2; 
						while (line[j] != ',') { 
							name[n] = line[j]; 
							n++; j++; 
						} 
						j--; 
            					name[n] = '\0'; 
						fi++; f += 2; 
					} 
				} 

				// Converting latitude and longitude in string to float. 
				lat2d = atof(latitude_as_string); 
				lon2d = atof(longitude_as_string); 
				distance_calculator(); 
			} 
		} 
		customer_list.close(); 
		out.close(); 
	} 
}; 

int main() { 
	json obj;  
	obj.json_parser(); 
	return 0; 
}