hdu 4386 Quadrilateral

内切圆的时候最大，公式为p = (a+b+c+d)/2   smax = aqrt((p-a)(p-b)(p-c)(p-d))

这是海伦公式的推广

#include<iostream>#include<cmath>using namespace std;int main(){int n, k = 1;scanf("%d", &n);while(n--){int i, a[5], max = 0;for(i = 0; i < 4; i++){scanf("%d", &a[i]);if(max < a[i])max = a[i];}if(a[0] + a[1] + a[2] + a[3] <= 2 * max){printf("Case %d: -1\n", k++);continue;}double p;p = (double)(a[0] + a[1] + a[2] + a[3]) / 2.0;printf("Case %d: %.6lf\n", k++, sqrt((p-a[0]) * (p-a[1]) * (p-a[2]) * (p-a[3])) );}return 0;}