原始ピタゴラス数探索ロジック：しらみつぶし編

PythagoraSwitch.java

import java.util.ArrayList;
import java.util.List;

public class PythagoraSwitch {

    public static void main(String[] args) {
        final int MAX = Integer.parseInt(args[0]);
        long start = System.nanoTime();
        List<PythagorasNum> result = new ArrayList<>();
        for (int c = 3; c <= MAX; c += 2) {
            long c2 = ((long) c) * c;
            for (int b = c - 1; true; b--) {
                long b2 = ((long) b) * b;
                long a2 = c2 - b2;
                if (a2 >= b2)
                    break;
                int a = (int) Math.sqrt(a2);
                if (((long) a) * a == a2 && isRelativelyPrime(c, b, a))
                    result.add(new PythagorasNum(a, b, c));
            }
        }
        long end = System.nanoTime();
        System.out.println(result);
        System.out.println("count:" + result.size());
        System.out.println("time:" + (end - start) / 1000000);
    }

    private static boolean isRelativelyPrime(int c, int b, int a) {
        return gcd(c, gcd(b, a)) == 1;
    }

    private static int gcd(int max, int min) {
        for (int residue; (residue = max % min) != 0; ) {
            max = min;
            min = residue;
        }
        return min;
    }

    private static class PythagorasNum {
        final int a;
        final int b;
        final int c;
        PythagorasNum(int a, int b, int c) {
            this.a = a;
            this.b = b;
            this.c = c;
        }
        @Override public String toString() {
            return "(" + a + ", " + b + ", " + c + ")";
        }
    }
}