doubt-area of a polygon

problem link:https://www.codechef.com/problems/R303
solution link:https://www.codechef.com/viewsolution/12854127
please help in finding the problem with my solution which is not being accepted

1 Like

If I am not wrong, the question gives you co-ordinates of polygon and asks area. I wrote a similar program last year, so have a look at my code in JAVA.
[PS - THIS PROGRAM WAS WRITTEN IN BLUEJ FOR MY OWN PURPOSES (helping in school homework :stuck_out_tongue: ). THE SYNTAX ETC. MAY NOT BE VALID ON CODECHEF IDE, SO SEE ACCORDINGLY.]

import java.util.*;
    class FunctionsArea
    {
         double area (int n)
        {
            System.out.println ("Enter x co-ordinates");
            int i,j,k,l;
            double area1=0.0 , area2=0.0;
            Scanner sc = new Scanner(System.in);
            double x[]= new double[n];
            double y[]= new double[n];
            for(i=0;i < n;++i)
            x[i]= sc.nextDouble();
            System.out.println ("Enter y co-ordinates");
            for (j=0;j < n;++j)
            y[j] = sc.nextDouble();
            for (k=0;k< n-1;k++)
            area1+= x[k]*y[k+1];
            for (l=0;l< n-1;l++)
            area2 += x[l+1]*y[l];
            area1= area1+ x[n-1]*y[0];
            area2+=x[0]*y[n-1];
            double area = (area1 - area2)/2;
            double ActualArea = Math.abs(area);
            System.out.println ("Area1 is "+area1+" "+"Area 2 is"+area2);
            return ActualArea;
        }
        public void main()
        {
            Scanner sc = new Scanner(System.in);
            System.out.println ("Enter number of sides");
            double area1,area2;
            int n =sc.nextInt();
            
            
            double NeededArea = area(n);
            
            System.out.println ("The area of figure is"+" "+NeededArea);
        }
    }

Area 1 and Area 2 were for debugging purposes, with Area= abs((Area1-Area2)/2)

Now, coming to your program, have a look at the test cases-

Compilation Successful
Input (stdin)
2
3
0 
0
1
1
2
1
3
1
1
-1
1
-1
0
Your Output
357180570621342400.0
357180570621342400.0

The above was result by compiling in hackerrank compiler, but codechef compiler also gave similar weird result. I suspect that the problem is in the formula-

while(c<=n)
 {
 if(i+1!=n)
 s+=((x[i]*y[i+1])-(y[i]*x[i+1]));
else
 s+=((x[i]*y[0])-(y[i]*x[0]));
i++;
 c++;
 }

c was 0. When the value of c is n, THE VALUE OF i IS ALSO N. And your if else EXECUTES.
n+1!=n = true

So, it uses a value which does not exist (i don’t know why array out of bound error isn’t thrown here!) but basically the thing is, a[n] doesn’t exist so any garbage value is assigned to it in the formula and its causing the error. That’s what i think.

thanks a lot.

Happy to help dear, :slight_smile:

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