给定需要出租车的人的GPS坐标(以度为单位)以及以JSON格式存储在文本文件中的城市中所有出租车的坐标，请在中找到可用的所有出租车司机的用户ID和名称50公里的距离。
例子：
Input : file customers.json which contains GPS co-ordinates of a person who needs a cab in degrees and co-ordinates of all the cabs in the city stored in a text file in JSON format.
Output : file answers.json which contains user-id and Name of all the cab drivers available in 50 km proximity stored in a new file.
使用的方法：
1.以字符串格式获取每个出租车的经度和纬度以及它们的经度
JSON编码的输入文件中的用户标识和名称。
2.将以字符串格式显示的出租车的经度和纬度转换为两倍。
3.转换用户和驾驶室中的乘员的纬度和经度
度到弧度。
4.使用Great Circle计算用户位置与驾驶室之间的距离
距离公式。
5.如果发现距离小于或等于50 kms，则输出用户-
出租车司机的ID和名称到新文件，否则不执行任何操作。
运行程序的步骤：
1.将代码和文件customer.json保存在同一位置。
2.现在，编译代码(使用cmd： g ++ file_name.cpp )并运行它(使用cmd： ./a.out /home/gfg/customers.json )，并传递文件名customer.json以及正确的位置(例如/home/gfg/customers.json)。
3.将在存在代码和customers.json文件的位置创建一个名为answers.json的文件。
// C++ code to find cabs nearby
#include
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
{
/* i and j are used to access various
elements of the char arrays. x is used
to measure the size of the element of
latitude_as_string array. y is used to
measure the size of the element of
longitude_as_string array. m is used
to measure the size of the element
of id_as_string array. n is used to
measure the size of the element of
name array. f keeps count of " " "
symbol. fi keeps count of " : " symbol.
*/
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;
// To get each line of customers.json
// file as string.
string line;
// Function to check whether distance between
// 2 points is less than 50km or not.
void distance_calculator()
{
if (distanceEarth(lat2d, lon2d) <= 50.0000)
{
// Converting id to int format.
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++;
// To get latitude of the location.
if (f == 3)
{
j++;
while (line[j] != '"')
{
latitude_as_string[x] = line[j];
x++; j++;
}
j--; latitude_as_string[x] = '\0';
}
// To get longitude of the location.
else if (f == 13)
{
j++;
while (line[j] != '"')
{
longitude_as_string[y] = line[j];
y++; j++;
}
j--; longitude_as_string[y] = '\0';
}
// To get id of the friend.
if (fi == 2)
{
j += 2;
while (line[j] != ',')
{
id_as_string[m] = line[j];
m++; j++;
}
j--; id_as_string[m] = '\0';
fi++;
}
// To get name of the friend.
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();
}
}
// closing stream of customer's file.
customer_list.close();
// closing stream of answer's file.
out.close();
}
};
int main()
{
// Creating object of the structure json
json obj;
// To read customers.json file.
obj.json_parser();
return 0;
}
输入文件(customers.json)：
{"latitude": "12.986375", "user_id": 12, "name": "Chris", "longitude": "77.043701"}
{"latitude": "11.92893", "user_id": 1, "name": "Alice", "longitude": "78.27699"}
{"latitude": "11.8856167", "user_id": 2, "name": "Ian", "longitude": "78.4240911"}
{"latitude": "12.3191841", "user_id": 3, "name": "Jack", "longitude": "78.5072391"}
{"latitude": "13.807778", "user_id": 28, "name": "Charlie", "longitude": "76.714444"}
{"latitude": "13.4692815", "user_id": 7, "name": "Frank", "longitude": "-9.436036"}
{"latitude": "14.0894797", "user_id": 8, "name": "Eoin", "longitude": "77.18671"}
{"latitude": "13.038056", "user_id": 26, "name": "Stephen", "longitude": "76.613889"}
{"latitude": "14.1225", "user_id": 27, "name": "Enid", "longitude": "78.143333"}
{"latitude": "13.1229599", "user_id": 6, "name": "Theresa", "longitude": "77.2701202"}
{"latitude": "12.2559432", "user_id": 9, "name": "Jack", "longitude": "76.1048927"}
{"latitude": "12.240382", "user_id": 10, "name": "Georgina", "longitude": "77.972413"}
{"latitude": "13.2411022", "user_id": 4, "name": "Ian", "longitude": "77.238335"}
{"latitude": "13.1302756", "user_id": 5, "name": "Nora", "longitude": "77.2397222"}
{"latitude": "13.008769", "user_id": 11, "name": "Richard", "longitude": "77.1056711"}
{"latitude": "13.1489345", "user_id": 31, "name": "Alan", "longitude": "77.8422408"}
{"latitude": "13", "user_id": 13, "name": "Olive", "longitude": "76"}
{"latitude": "11.999447", "user_id": 14, "name": "Helen", "longitude": "-9.742744"}
{"latitude": "12.966", "user_id": 15, "name": "Michael", "longitude": "77.463"}
{"latitude": "12.366037", "user_id": 16, "name": "Ian", "longitude": "78.179118"}
{"latitude": "14.180238", "user_id": 17, "name": "Patricia", "longitude": "-5.920898"}
{"latitude": "13.0033946", "user_id": 39, "name": "Lisa", "longitude": "77.3877505"}
{"latitude": "12.228056", "user_id": 18, "name": "Bob", "longitude": "76.915833"}
{"latitude": "14.133333", "user_id": 24, "name": "Rose", "longitude": "77.433333"}
{"latitude": "55.033", "user_id": 19, "name": "Enid", "longitude": "78.112"}
{"latitude": "13.121111", "user_id": 20, "name": "Enid", "longitude": "-9.831111"}
{"latitude": "11.802", "user_id": 21, "name": "David", "longitude": "-9.442"}
{"latitude": "14.374208", "user_id": 22, "name": "Charlie", "longitude": "78.371639"}
{"latitude": "13.74412", "user_id": 29, "name": "Oliver", "longitude": "76.11167"}
{"latitude": "13.761389", "user_id": 30, "name": "Nick", "longitude": "76.2875"}
{"latitude": "14.080556", "user_id": 23, "name": "Eoin", "longitude": "77.361944"}
{"latitude": "12.833502", "user_id": 25, "name": "David", "longitude": "78.122366"}
输出文件(answers.json)：
{"user_id": 6, "name": "Theresa"}
{"user_id": 5, "name": "Nora"}
{"user_id": 31, "name": "Alan"}
{"user_id": 15, "name": "Michael"}
{"user_id": 39, "name": "Lisa"}
参考：大圆距离
想要从精选的最佳视频中学习并解决问题，请查看有关从基础到高级C++的C++基础课程以及有关语言和STL的C++ STL课程。要完成从学习语言到DS Algo等的更多准备工作，请参阅“完整面试准备课程” 。