Sorting points (x,y) according to the angle made with +ve x-axis

general
1

I am unable to identify error in my code
Question-https://www.hackerrank.com/contests/brandeiscodesprint/challenges/polar-angles
my code:

#include <bits/stdc++.h>
using namespace std;
typedef long long int lli;
#define PI 3.14

int main()
{
    lli n;
    cin>>n;
    pair <  pair <float,float> , pair <lli,lli> > a[n];
    float theta,dist;
    for(lli i=0;i<n;i++)
    {
        cin>>a[i].second.first>>a[i].second.second;
        if(a[i].second.second==0){
            if(a[i].second.first>0) theta=0;
            else theta=PI;
    }
        else if(a[i].second.first==0){
            if(a[i].second.second>0) theta=(float)((float)(90*PI)/(float)180);
            else theta=(float)((float)(270*PI)/(float)180);
        }
        else{
            float temp=(float)((float)a[i].second.second/(float)a[i].second.first);
           //cout<<(float)atan(temp)<<endl;
            if(a[i].second.first>0){
                if(a[i].second.second>0){
                    theta=(float)atan(temp);
                }else{
                    theta=(float)((float)(2*PI)+(float)atan(temp));
                }
            }else{
                if(a[i].second.second>0){
                     theta=(float)((float)PI+(float)atan(temp));
                }else{
                    theta=(float)((float)PI+(float)atan(temp));
                }
            }
        }

        dist=(float)((float)(a[i].first.first*a[i].first.first)+(float)(a[i].first.second*a[i].first.second));
        a[i].first.first=(float)theta;
        a[i].first.second=(float)dist;
        cout<<theta<<endl;
    }
    sort(a,a+n);
    for(lli i=0;i<n;i++){
        cout<<a[i].second.first<<" "<<a[i].second.second<<endl;
    }
return 0;
}
2

What is the Problem you are facing ? Is it a Wrong Answer ? Is it a compilation error ? Is it a Runtime Error ? Please specify that

3

I think it might be the result of smaller precision… Use double instead…By the way if I had that question I would have had solvedd it on the basis of co ordiantes :slight_smile:

4

Hi, this part of code will work :

  int N; // Number of points.
  double dx, dy, temp;  //dx, dy are coordinate points.
  vector < pair < double, pair < double, double > > > angles; // A vector which holds the angles, points.

  for(LL n = 0; n < N; ++n){
     scanf("%lf%lf", &dx, &dy);
     temp = atan2(dy, dx);
     angles.pb(make_pair(temp, make_pair(dx, dy));
  }
  sort(angles.begin(), angles.end()); // Now sorting the angles. Based on angle.

As a whole atan2(y, x) will take care of all the conversions. i.e it returns the angle made by the required point (x, y) with +X axis.

5

Thanx a lot! Precision does matter.

6

Thank you.atan2() is a something new to learn for me.Better than the long code i wrote!
BTW my mistake was in calculating the distance.Thanks a lot!