If it is impossible to find out the distance from C to D, then write "Impossible." and not "Impossible"

use cout.precision(0) and cout << sqrt(ans) * 1000.0 << endl;

Edited by author 09.02.2020 20:13

I just used some identities and solved some equations to get the answer. Pretty sure I wouldn't be able to solve if I did not have access to the net and that is pretty lame :/

Was anybody able to solve by deriving the solution themselves? If yes, then please share! I want to learn the approach! ^_^

My simple wrong program skips necessary mathematical checks, but it got AC.

1 20 5 5
Answer: Impossible.
(Wrong solution skipped the check of cos(∠DAC) bounds; a cosinus must be from -1 to 1)

5 7 4 7
Answer: Impossible.
(Wrong solution skipped the check of the order of satelites; the test case is from the task subscription, I've just changed the positions of A and B satelites).

import math
values = raw_input().split(' ')
a = float(values[0])
b = float(values[1])
c = float(values[2])
d = float(values[3])
if (math.fabs(a*b-c*d)<0.001):
    print "Impossible."

j = 0.0
x = a**2 + b**2 #DC**2(1)
y = c**2 + d**2 #DC**2(2)
x1 = - 2 * a * b
y1 = - 2 * c * d
l = math.fabs(x - y)
r = math.fabs(x1 - y1)
if r == 0:
    False
else:
    j = l / r #cos
    res = a**2.0 + b**2.0 - 2.0 * a * b *j #DC**2
    res = math.sqrt(res)*1000 #DC
    print "Distance is %(res)d km." %{"res": res}


Edited by author 29.04.2016 15:30

Edited by author 29.04.2016 16:01

I took into account all recomendations from discussions of this problem, but still have WA#6. Does anybody know this test?

Give me tests!

var
 AD,AC,BD,BC,X,Y:int64;
 CD:real;

BEGIN
 read(AD,AC,BD,BC);

 X:=AD*AC-BD*BC;
 Y:=AD*AC*(BD*BD+BC*BC)-BD*BC*(AD*AD+AC*AC);
 if(X=0)or(Y*X<0) then write('Impossible.')
 else begin
  write('Distance is ');
  CD:=1000*sqrt(Y/X);
  write(CD:0:0,' km.');
 end;
END.

* don't use double (use float)
* don's foget fabs()

1294. Mars Satellites    G++ 4.7.2    Accepted    0.015    345 KB
1294. Mars Satellites    G++ 4.7.2 C++11    Wrong answer    1    0.015    369 KB

my code c#


using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;


namespace kyrsach1294
{
    class Program
    {
        static int Main(string[] args)
        { int a,b,c,d;
            string[] dlins = Console.ReadLine().Split(' ');
         a = int.Parse(dlins[0]);
         b = int.Parse(dlins[1]);
         c = int.Parse(dlins[2]);
         d = int.Parse(dlins[3]);
         if (a * b==c * d)
         {
             {
                 Console.WriteLine("Impossible.");
                 return 0;
             }
         }


       double s,s1,s2;
       s1 = c * d / (c * d - a * b);

        s2 = a * b / (c * d - a * b);
       s = s1*a*a+s1*b*b-s2*c*c-s2*d*d;
            if (s < 0)
            {
                Console.WriteLine("Impossible.");
                return 0;
            }
            int answer;

            s = Math.Sqrt(s) * 1000;
            answer = Convert.ToInt32(s);
            Console.WriteLine("Distance is "+answer+" km.");
            return 0;
        }
    }
}
please help

Edited by author 03.04.2012 22:40

{$N+}
Program Mars_satellites;

 Var
   cos_,x,a,b,c,d:Double;

Begin
  Readln(a,b,c,d);
  If (a*b-c*d)=0 Then
  Begin
    Write('Impossible');
  End
  Else
  Begin
    cos_:=a*a+b*b-c*c-d*d;
    cos_:=cos_/(2*a*b-2*c*d);
    x:=a*a+b*b-2*a*b*cos_;
    x:=sqrt(x);
    x:=round(1000*x);
    Write('Distance is ',x:0:0,' km.');
  End;
End.

what is wrong???

#include <iostream>
#include <cmath>
using namespace std;

int main ()
{
    int a, b, c, d;
    cin >> a >> b >> c >> d;
    if (a*b == c*d)
    {
        cout << "Impossible.";
        return 0;
    }

    double s;
    s = (c*d*a*a + c*d*b*b - a*b*c*c - a*b*d*d)/(c*d-a*b);
    if (s < 0)
    {
        cout << "Impossible.";
        return 0;
    }

    int ans;
    s = (sqrt(s) * 1000);
    if (s - (int)s < 0.5)
        ans = (int)s;
    else
        ans = (int)s + 1;
    cout << "Distance is " << ans << " km.";
    return 0;
}

Edited by author 26.02.2012 18:37

1. ABCD is the only allowed order (not ADBC)
2. Use cosinuse rule, and if you get division by zero... so sutuation is impossible
3. Be carefull while checking zero... use integers or compare with EPS
4. printf("... %.0lf ...", res)
5. Check your output format twice
good luck

The printing of the answer in C++ should be, e.g., in the form:
cout << "Distance is "
     << setiosflags(std::ios_base::fixed)
     << setprecision(0)
     << 1000.0*sqrt(dist) << " km.";
where dist is double value. You don't need to round off the answer with the help of some functions.

In this problem,rounding the double value to the nearest integer appeares to be the most tricky part of the whole problem.
If you want to guarantee correct rounding, do it yourself with floor() and ceil().
At least,as it happened to me.:)

(or to people who put the text of the problem here).

The text of the problem not seems to be correct.
You can't say 'geostationery orbit', when you mean Mars. You should say 'marsostationary orbit' or something like that.

Edited by author 09.01.2009 12:42

What's wrong???

my code:

#include <cstdio>
#include <cmath>

int main() {
  int a, b, c, d;
  scanf("%d %d %d %d", &a, &b, &c, &d);

  if (a * b == c * d) {
    printf("Impossible.\n");
  } else {
    double cos = (a * a * 1.0 + b * b - c * c - d * d) / (2 * a * b - 2 * c * d);
    double x = a * a * 1.0 + b * b - 2 * a * b * cos;

    if (x < 0)
      printf("Impossible.\n");
    else
      printf("Distance is %d km.\n", (int)(sqrt(x) * 1000));
  }
}

It's a very easy problem bur needs much attention.
I got WA many times just for small things:
1) "Impossible." its not "Impossible"
2) Input data order
3) Precision
4) Not writing "Distance is..."