HDU 6219

/*最大凸包*/
#include <stdio.h>
#include <string.h>
#include <algorithm>
using namespace std;

const int maxsz = 55;
int m, dp[maxsz][maxsz], ans;
struct Point {
    int x, y;
    Point ( int xx = 0, int yy = 0 ) : x(xx), y(yy){};
    Point operator + (const Point p ) { return Point ( x + p.x, y + p.y ) ; }
    Point operator - (const Point p ) { return Point ( x - p.x, y - p.y ) ; }
}point[maxsz], t[maxsz];
int Dot ( Point i, Point j ) {
    return i.x * j.x + i.y * j.y;
}
int Cross ( Point i, Point j ) {
    return i.x * j.y - i.y * j.x;
}
bool cmp1 ( const Point &i, const Point &j ) {
    return  i.y == j.y ? i.x < j.x : i.y < j.y;
}
bool cmp2 ( const Point &i, const Point &j ) {
    return Cross (i, j) == 0 ? Dot (i, i) < Dot (j, j) : Cross (i, j) > 0;
}
void solve () {
    for (int i = 0; i <= m; i++) {
        for (int j = i; j <= m; j++)
            dp[i][j] = dp[j][i] = 0;
    }
    for (int i = 2; i <= m; i++) {
        for (int j = 1; j < i; j++) {
            if (Cross(t[i], t[j]) == 0) continue;
            bool emp = 1;// in triangle
            for (int k = j + 1; k < i; k++) {
                if (Cross(t[k], t[i]) > 0 && Cross (t[j], t[k]) > 0 && Cross (t[i] - t[j], t[k] - t[j]) > 0)
                    emp = 0;
            }
            if (!emp) continue;
            int area = Cross (t[j], t[i]);
            dp[i][j] = area;
            if (Cross(t[j], t[j-1])) {//共线 
                for (int k = 1; k < j; k++) {
                    if (Cross(t[k] - t[i], t[j] - t[i]) > 0)
                        dp[i][j] = max(dp[i][j], dp[j][k] + area);
                }
            }
            ans = max(ans, dp[i][j]);
        }
    }
}
int main () {
    int T, n;
    scanf("%d", &T);
    while (T--) {
        scanf("%d", &n);
        for (int i = 1; i <= n; i++) scanf("%d%d", &point[i].x, &point[i].y);
        sort ( point + 1, point + 1 + n, cmp1);// sort LTL
        ans = 0;
        for (int i = 1; i <= n-2; i++, m = 0) {
            for (int j = i + 1; j <= n; j++) t[++m] = point[j] - point[i];
            sort ( t + 1, t + 1 + m, cmp2);// sort angle
            solve();
        }
        printf("%.1lf
", 1.0 * ans / 2);
    }
    return 0;
}