pku 1687(求面积最大的多边形的编号)

/*
*  题目要求：求面积最大的那个面的编号
*  方法：分别求每个面的面积，并比较最大的面积 
*/
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <iostream>

using namespace std;

const int N = 55;

struct point {
    int x;
    int y;
}p[N], sp[N];

double crossProd(point A, point B, point C) {
    return (B.x-A.x)*(C.y-A.y) - (B.y-A.y)*(C.x-A.x);
}

int main() {
    int t;
    scanf ("%d", &t);
    while (t--) {
        int n;
        scanf ("%d", &n);
        for (int i=1; i<=n; ++i) scanf ("%d%d", &p[i].x, &p[i].y);
        int m;
        scanf ("%d", &m);
        double maxArea = 0;
        int ans = 0;
        for (int j=1; j<=m; ++j) {
            int cs, num;
            scanf ("%d", &cs);
            int k = 0;
            for (int i=0; i<cs; ++i) {
                scanf ("%d", &num);
                sp[k++] = p[num];
            }
            double area = 0;
            for (int i=2; i<k; ++i) area += crossProd(sp[0], sp[i-1], sp[i]);
            if (maxArea < fabs(area)) {
                maxArea = fabs(area);
                ans = j;
            }
        }
        printf ("%d\n", ans);
    }
}