Fzu problem 2148 moon game (judgement convex quadrilateral)

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Question: Give You N points to determine the number of convex quadrants that can be formed.

Idea: If a concave quadrilateral is formed, it indicates that a point is inside the triangle connected by the other three points. In this way, you only need to determine the area of the three triangles connected to each of the other three points and the area of the triangle composed of the other three points.

I forgot to add FABS in the middle, and I still made a mistake several times.

 1 //FZU2148 2 #include <cstdio> 3 #include <cstring> 4 #include <iostream> 5 #include <cmath> 6 #define eps  1e-9 7 #define zero(x) (((x)>0? (x) : (-x)) < eps ) 8  9 using namespace std ;10 11 struct point{double x;double y ;}p[32];12 struct Line{point a;point b;};13 14 double area(point a,point b,point c)15 {16     return a.x * b.y + c.x * a.y + b.x * c.y - c.x * b.y - a.x * c.y - b.x * a.y ;17 }18 bool judge(point a,point b,point c,point d)19 {20     double sum = fabs(area(a,b,c))+fabs(area(a,b,d))+fabs(area(a,c,d)) ;21     double sun = fabs(area(b,c,d)) ;22     if(fabs(sum-sun) <eps) return true ;23     return false ;24 }25 bool solve(point a,point b,point c,point d)26 {27     if(judge(a,b,c,d) || judge(b,a,c,d) || judge(c,b,a,d) || judge(d,b,c,a)) return false ;28     return true ;29 }30 int main()31 {32     int T,casee = 1, n;33     scanf("%d",&T) ;34     while(T--)35     {36         scanf("%d",&n) ;37         for(int i = 0 ; i < n ; i++)38             scanf("%lf %lf",&p[i].x,&p[i].y) ;39         int ans = 0 ;40         for(int i = 0 ; i < n ; i++)41         {42             for(int j = i+1 ; j < n ; j++)43             {44                 for(int k = j + 1 ; k < n ; k++)45                 {46                     for(int h = k+1 ; h < n ; h++)47                     {48                         if(solve(p[i],p[j],p[k],p[h])) ans ++ ;49                     }50                 }51             }52         }53         printf("Case %d: %d\n",casee ++ ,ans) ;54     }55     return 0 ;56 }

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