Problem 91 - Java

After freeing up Java, I decided to use it. Problem 91 was not particularly hard (most of the recent problems have mostly been a matter o knowing how to enumerate the answer space well, and how to check for the answer easily arithmetically), so I actually did not intend to use a language as useful as Java on it. However, Java was available, and the first two languages I tried I ran into difficulties with (I may use them eventually, but Factor documentation was not very useful, and Dylan is having difficulties building on my machine).

Also, solving 91 in Java results in the nice phenomenon of using Java Byecode and Java to solve consecutive problems. Anyway, the main difficulty I experienced trying to solve this problem was me accidentally expressing the condition for perpendicularity incorrectly. I accidentally took the reciprocal twice, causing me to be checking if slopes were negatives, instead of negative reciprocals. other than that and other small issues, this was not the hardest of problems.

Runs in about .15s on my machine.

public class e91 {

    public static int min (int x, int y) {
        return x < y ? x : y;
    }

    public static void main(String[] args) {

        int ans = 0;
        final int B = 50 + 1;
        for (int P1 = 1; P1 < B*B; ++P1) {
            for (int P2 = P1 + 1; P2 < B*B; ++P2) {
                int x1 = P1 / B;
                int y1 = P1 % B;
                int x2 = P2 / B;
                int y2 = P2 % B;
                int oldans = ans; 
                if(min(x1, x2) == 0 && min(y1, y2) == 0) {
                    //Right Angle at origin
                    ++ans;
                } else if ((y1 == y2) && (x1 == 0 || x2 == 0)) {
                    //undef slope, check explicitly
                    ++ans;
                } else if ((x1 == x2) && (y1 == 0 || y2 == 0)) {
                    //same
                    ++ans;
                } else {
                    //Negative reciprocals => right angle
                    int num   = y1 * (y1 - y2);
                    int denom = x1 * (x1 - x2);
                    if (denom != 0) {
                        int ratio = num / denom;
                        int rem   = num % denom;
                        ans += (ratio == -1 && rem == 0) ? 1 : 0;
                    }
                    if (ans == oldans) {
                        num   = y2 * (y2 - y1);
                        denom = x2 * (x2 - x1);
                        if (denom != 0) {
                            int ratio = num / denom;
                            int rem   = num % denom;
                            ans += (ratio == -1 && rem == 0) ? 1 : 0;
                        }
                    }
                }
            }
        }
        System.out.println(ans);
    }
}