http://poj.org/problem?id=2187
求出形成凸包的各边 找出最大的
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1 #include <iostream> 2 #include<cstdio> 3 #include<string.h> 4 #include<algorithm> 5 using namespace std; 6 struct node 7 { 8 int x,y; 9 }q[50011]; 10 int dis(int x1,int y1,int x2,int y2) 11 { 12 return (x1-x2)*(x1-x2)+(y1-y2)*(y1-y2); 13 } 14 node st[50011]; 15 bool cmp(node a,node b) 16 { 17 if((a.x-q[1].x)*(b.y-q[1].y)==(a.y-q[1].y)*(b.x-q[1].x)) 18 return dis(a.x,a.y,q[1].x,q[1].y)<dis(b.x,b.y,q[1].x,q[1].y); 19 else 20 return (a.x-q[1].x)*(b.y-q[1].y)>(a.y-q[1].y)*(b.x-q[1].x); 21 } 22 int judge(node a,node b,node c) 23 { 24 if((a.x-b.x)*(c.y-a.y)-(c.x-a.x)*(a.y-b.y)>0) 25 return 1; 26 else 27 return 0; 28 } 29 int main() 30 { 31 int i,j,k =1,n,m,top =1; 32 node t; 33 scanf("%d",&n); 34 for(i = 1 ; i <= n ;i++) 35 { 36 scanf("%d%d",&q[i].x,&q[i].y); 37 if(q[i].y<q[k].y||(q[i].y==q[k].y&&q[i].x<q[k].x)) 38 k = i; 39 } 40 if(k!=1) 41 { 42 t = q[1]; 43 q[1] = q[k]; 44 q[k] = t; 45 } 46 sort(q+2,q+n+1,cmp); 47 st[top++] = q[1]; 48 st[top++] = q[2]; 49 st[top++] = q[3]; 50 for(i = 4; i <= n ;) 51 { 52 if(top<3||judge(st[top-1],st[top-2],q[i])) 53 { 54 st[top++] = q[i++]; 55 } 56 else 57 { 58 top--; 59 } 60 } 61 int ma = 0; 62 st[top] = q[1]; 63 for(i = 1 ; i < top ; i++) 64 { 65 for(j = i+1 ; j < top ; j++) 66 { 67 ma = max(ma,dis(st[i].x,st[i].y,st[j].x,st[j].y)); 68 } 69 } 70 printf("%d\n",ma); 71 return 0; 72 }
http://poj.org/problem?id=1113
一样是凸包 这个总长比凸包的总长正好大了以L为半径的圆 这个看题上的那个图 很好想
直接拿上面的改一下 距离换成double 这里WA了好多次
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1 #include <iostream> 2 #include<cstdio> 3 #include<string.h> 4 #include<algorithm> 5 #include<cmath> 6 #define PI 3.141592653 7 using namespace std; 8 struct node 9 { 10 int x,y; 11 }q[50011]; 12 double dis(int x1,int y1,int x2,int y2) 13 { 14 double x = x1-x2; 15 double y = y1-y2; 16 return sqrt(x*x+y*y); 17 } 18 node st[50011]; 19 bool cmp(node a,node b) 20 { 21 if((a.x-q[1].x)*(b.y-q[1].y)==(a.y-q[1].y)*(b.x-q[1].x)) 22 return dis(a.x,a.y,q[1].x,q[1].y)<dis(b.x,b.y,q[1].x,q[1].y); 23 else 24 return (a.x-q[1].x)*(b.y-q[1].y)>(a.y-q[1].y)*(b.x-q[1].x); 25 } 26 int judge(node a,node b,node c) 27 { 28 if((a.x-b.x)*(c.y-a.y)-(c.x-a.x)*(a.y-b.y)>0) 29 return 1; 30 else 31 return 0; 32 } 33 int main() 34 { 35 int i,j,k =1,n,m,top =1,l; 36 node t; 37 while(scanf("%d%d",&n,&l)!=EOF) 38 { 39 top = 1; 40 for(i = 1 ; i <= n ;i++) 41 { 42 scanf("%d%d",&q[i].x,&q[i].y); 43 if(q[i].y<q[k].y||(q[i].y==q[k].y&&q[i].x<q[k].x)) 44 k = i; 45 } 46 if(k!=1) 47 { 48 t = q[1]; 49 q[1] = q[k]; 50 q[k] = t; 51 } 52 sort(q+2,q+n+1,cmp); 53 st[top++] = q[1]; 54 st[top++] = q[2]; 55 st[top++] = q[3]; 56 for(i = 4; i <= n ;) 57 { 58 if(top<3||judge(st[top-1],st[top-2],q[i])) 59 { 60 st[top++] = q[i++]; 61 } 62 else 63 { 64 top--; 65 } 66 } 67 st[top] = q[1]; 68 double ma; 69 ma = 2*PI*l; 70 for(i = 1 ; i < top ; i++) 71 { 72 ma += dis(st[i].x,st[i].y,st[i+1].x,st[i+1].y); 73 } 74 printf("%.0f\n",ma); 75 } 76 return 0; 77 }