TriangleWithMaximumPerimeter.java

public class TriangleWithMaximumPerimeter {
    
    public static void main(String[] args) {
        var scanner = new java.util.Scanner(System.in);

        var n = scanner.nextInt();

        int[][] points = new int[n][2];

        for (int i = 0; i < n; i++) {
            points[i][0] = scanner.nextInt();
            points[i][1] = scanner.nextInt();
        }

        double maxPerimeter = 0;
        for (int i = 0; i < n - 2; i++) {
            for (int j = i + 1; j < n - 1; j++) {
                for (int k = j + 1; k < n; k++) {
                    var perimeter = calculatePerimeter(points[i], points[j], points[k]);
                    maxPerimeter = Math.max(maxPerimeter, perimeter);
                }
            }
        }
        System.out.printf("%.15f%n", maxPerimeter);
    }

    private static double calculatePerimeter(int[] p1, int[] p2, int[] p3) {
        var side1 = calculateDistanceBetweenPoints(p1, p2);
        var side2 = calculateDistanceBetweenPoints(p2, p3);
        var side3 = calculateDistanceBetweenPoints(p3, p1);
        return side1 + side2 + side3;
    }

    private static double calculateDistanceBetweenPoints(int[] p1, int[] p2) {
        var dx = p2[0] - p1[0];
        var dy = p2[1] - p1[1];
        return Math.sqrt(dx * dx + dy * dy);
    }
}