POJ 1113

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http://poj.org/problem?id=1113

求离多边形的距离至少为L的多边形的最小周长

先求凸包

#include<stdio.h>#include<math.h>#include<string.h>#include<algorithm>#define eps 1e-8#define PI 3.1415926#define M 2005using namespace std;struct point{int x;int y;}po[M],stack[M];bool cmp(point a,point b){if(a.y==b.y)return a.x<b.x;return a.y<b.y;}double Getlen(point a,point b){return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));}bool mult(point sp,point ep,point op){return (sp.x-op.x)*(ep.y-op.y)>=(ep.x-op.x)*(sp.y-op.y);}int Graham(point pnt[],int n,point res[]){int i,len,k=0,top=1;sort(pnt,pnt+n,cmp);if(n==0) return 0;res[0]=pnt[0];if(n==1) return 1;res[1]=pnt[1];if(n==2) return 2;res[2]=pnt[2];for(i=2;i<n;i++){while(top && mult(pnt[i],res[top],res[top-1]))top--;res[++top]=pnt[i];}len=top;res[++top]=pnt[n-2];for(i=n-3;i>=0;i--){while(top!=len && mult(pnt[i],res[top],res[top-1]))top--;res[++top]=pnt[i];}return top;}int main(){int i,j;int top;int n,L;double sum;__int64 sum1;while(scanf("%d%d",&n,&L)!=EOF){ for(i=0;i<n;i++)scanf("%d%d",&po[i].x,&po[i].y);top=Graham(po,n,stack);sum=0;sum=sum+Getlen(stack[0],stack[top-1])*1.0;for(i=1;i<top;i++){sum=sum+Getlen(stack[i],stack[i-1]);}sum=sum+2*PI*L;sum1=(__int64)sum;if((sum-sum1*1.0)>=0.5+eps)sum1+=1;printf("%I64d\n",sum1);}return 0;}