Passed all but one test case:

// Complete the solve function below.
static String solve(int d, int k) {
        //get integer format of radius
        int r = (int)Math.sqrt(d); 

        int count = 0;

        //loop for all integer values on X axis
        for(int i = -r; i<r; i++){

                //calculate the float/double value of Y
                // Let's say, it could be 2.0 or 2.3
                double y = Math.sqrt(d - i*i);

            // convert to INT so it will become either 2.0 in above cases
                int intY = (int)y;

                //now compare the int version with original version.
                //if they are same, then Y is also integer and hence we got our point on
                //the circle. Count is incremented by 2 because, this new point is applicable both above and below x axis.
                if((float)intY == y ){
                        count+=2;
                }

        }  
        if(k >= count){
                return "possible";
        } else {
                return "impossible";

    }  
}