Main.java

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

public class Main {

    public static void main(String[] args) {
        System.out.println("Starting program...");
        int n = readFromKeyboard();
        long start = System.nanoTime();
        List<List<Integer>> triples1 = pythagoreanTriple(n);
        long end = System.nanoTime();
        
        System.out.printf(
                "pythagoreanTriple(%d) in %.1f milliseconds.\n",
                n, 
                (end - start) / 1e6);
        
        start = System.nanoTime();
        List<List<Integer>> triples2 = pythagoreanTriple2(n);
        end = System.nanoTime();
        
        System.out.printf(
                "pythagoreanTriple2(%d) in %.1f milliseconds.\n",
                n, 
                (end - start) / 1e6);
        System.out.println("Algorithms agree: " + triples1.equals(triples2));
    }

    private static int readFromKeyboard() {
        Scanner keybInput = new Scanner(System.in);
        return keybInput.nextInt();
    }

    private static List<List<Integer>> pythagoreanTriple(int n) {
        //List<List<Integer>> pytTri = new ArrayList<List<Integer>>();
        // Use diamond inference istead:
        List<List<Integer>> pytTri = new ArrayList<>();
        int i, j, k;
        for (i = 3; i < n; i++) {
            for (j = n; j > i; j--) {
                for (k = n; k > j; k--) {
                    if (i * i + j * j == k * k) {
                        ArrayList<Integer> tempArray = new ArrayList<Integer>(); //we create a list of integers
                        tempArray.add(i);
                        tempArray.add(j);
                        tempArray.add(k);
                        pytTri.add(tempArray);
                    }
                }
            }
        }
        return pytTri;
    }

    private static List<List<Integer>> pythagoreanTriple2(int n) {
        List<List<Integer>> pytTri = new ArrayList<>();
        
        for (int i = 3; i < n; i++) {
            int iSquared = i * i;
            
            for (int j = n; j > i; j--) {
                int iSquaredPlusJSquared = iSquared + j * j;
                
                for (int k = n; k > j; k--) {
                    if (iSquaredPlusJSquared == k * k) {
                        List<Integer> result = new ArrayList<>(3);
                        result.add(i);
                        result.add(j);
                        result.add(k);
                        pytTri.add(result);
                    }
                }
            }
        }
        
        return pytTri;
    }
    
    private static void printResult(List<List<Integer>> resultList) {
        for (List<Integer> ls : resultList) {
            for (Integer i : ls) {
                System.out.print(i);
                System.out.print(" ");
            }
            System.out.println(";");
        }
    }
}