1 #include<iostream> 2 #include<vector> 3 #include<algorithm> 4 #include<math.h> 5 using namespace std; 6 7 struct point 8 { 9 double x; 10 double y; 11 double angle; 12 }; 13 //判断点A，D是否在点B，C连线的两侧 14 bool different(point A,point B,point C,point D) 15 { 16 double x1=A.x,x2=B.x,x3=C.x,x4=D.x; 17 double y1=A.y,y2=B.y,y3=C.y,y4=D.y; 18 if(x3==x2) 19 { 20 if((x1-x2)*(x4-x2)<0) 21 return true; 22 else 23 return false; 24 } 25 else 26 { 27 if((((x1-x2)*(y3-y2)+y2*(x3-x2))/(x3-x2))*(((x4-x2)*(y3-y2)+y2*(x3-x2))/(x3-x2))<0) 28 return true; 29 else return false; 30 } 31 } 32 double my_angle(point A,point B) 33 { 34 if(A.x==B.x && A.y==B.y) 35 return 0; 36 return acos((B.x-A.x)/(sqrt((B.y-A.y)*(B.y-A.y)+(B.x-A.x)*(B.x-A.x)))); 37 } 38 bool ismin(point A,point B) 39 { 40 return A.y<B.y; 41 } 42 bool isAngle(point A,point B) 43 { 44 return A.angle<B.angle; 45 } 46 int main() 47 { 48 vector<point> num; 49 int x,y; 50 char c; 51 while(cin>>x>>y) 52 { 53 point temp; 54 temp.x=x; 55 temp.y=y; 56 temp.angle=0; 57 num.push_back(temp); 58 cin.get(c); 59 if(c==' ') 60 break; 61 } 62 sort(num.begin(),num.end(),ismin); 63 point first=num[0]; 64 for(vector<point>::iterator iter=num.begin();iter!=num.end();iter++) 65 { 66 (*iter).angle=my_angle(first,*iter); 67 } 68 sort(num.begin(),num.end(),isAngle); 69 vector<point> result; 70 result.push_back(num[0]); 71 result.push_back(num[1]); 72 for(int i=2;i<num.size()-1;i++) 73 { 74 if(!different(num[i-2],num[i-1],num[i],num[i+1])) 75 result.push_back(num[i]); 76 } 77 result.push_back(num[num.size()-1]); 78 for(int p=0;p<result.size();p++) 79 { 80 cout<<result[p].x<<" "<<result[p].y<<endl; 81 } 82 system("pause"); 83 return 0; 84 }