how is this cpp code running without a main function?

Question

topcoder problem BearNSWE submitted by zig_zag

#include <set>
#include <map>
#include <stack>
#include <queue>
#include <cmath>
#include <ctime>
#include <vector>
#include <cstdio>
#include <string>
#include <climits>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;

double xx, yy;

class BearNSWE
{
public:
    double totalDistance(vector <int> a, string dir)//no main function
  {
    int n = a.size();
    double ans = 0.0;
    xx = yy = 0.0;
    for (int i = 0; i < n; i++)
    {
      if (dir[i] == 'N')
      {
        yy = yy + a[i];
      }
      else if (dir[i] == 'S')
      {
        yy = yy - a[i];
      }
      else if (dir[i] == 'W')
      {
        xx = xx - a[i];
      }
      else if (dir[i] == 'E')
      {
        xx = xx + a[i];
      }
      ans = ans + a[i];
    }
    return ans + sqrt(xx*xx + yy*yy);
  }
};

Answer 1

The topcoder runner expects a class with a specific method interface, it is specified in the problem statement. For this specific problem, it is here.

Topcoder will compile this code with additional sources - a main method, which runs the examples - added.

If you want to test your code locally in the topcoder editor (or just autogenerate the code for running it), there are several plugins available for it, for example the ExampleBuilder.