Solution.java

class Solution {
    public double minAreaFreeRect(int[][] points) {
        int n = points.length;
        Set<Integer> s = new HashSet<>(n);
        for (int[] p : points) {
            s.add(f(p[0], p[1]));
        }
        double ans = Double.MAX_VALUE;
        for (int i = 0; i < n; ++i) {
            int x1 = points[i][0], y1 = points[i][1];
            for (int j = 0; j < n; ++j) {
                if (j != i) {
                    int x2 = points[j][0], y2 = points[j][1];
                    for (int k = j + 1; k < n; ++k) {
                        if (k != i) {
                            int x3 = points[k][0], y3 = points[k][1];
                            int x4 = x2 - x1 + x3, y4 = y2 - y1 + y3;
                            if (s.contains(f(x4, y4))) {
                                if ((x2 - x1) * (x3 - x1) + (y2 - y1) * (y3 - y1) == 0) {
                                    int ww = (x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1);
                                    int hh = (x3 - x1) * (x3 - x1) + (y3 - y1) * (y3 - y1);
                                    ans = Math.min(ans, Math.sqrt(1L * ww * hh));
                                }
                            }
                        }
                    }
                }
            }
        }
        return ans == Double.MAX_VALUE ? 0 : ans;
    }

    private int f(int x, int y) {
        return x * 40001 + y;
    }
}