鍑稿寘鐩村緞 diameter of a convex polygon
#include <cstdlib>#include<iostream>#include<cmath>using namespace std;#define MAXN 50005#define eps 1e-8#define zero(x) (((x)>0?(x):-(x))<eps)
struct point{double x,y;}p5[MAXN],convex1[MAXN];;//璁＄畻cross product (P1-P0)x(P2-P0)double xmult(point p1,point p2,point p0){
return (p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.x)*(p1.y-p0.y);
}double dist(point p3,point p4){ return (p3.x-p4.x)*(p3.x-p4.x)+(p3.y-p4.y)*(p3.y-p4.y);}//graham綆楁硶欏烘椂閽堟瀯閫犲寘鍚墍鏈夊叡綰跨偣鐨勫嚫鍖?O(nlogn)point p1,p2;int graham_cp(const void* a,const void* b){ double ret=xmult(*((point*)a),*((point*)b),p1); return zero(ret)?(xmult(*((point*)a),*((point*)b),p2)>0?1:-1):(ret>0?1:-1);}void _graham(int n,point* p,int& s,point* ch){ int i,k=0; for (p1=p2=p[0],i=1;i<n;p2.x+=p[i].x,p2.y+=p[i].y,i++) if (p1.y-p[i].y>eps||(zero(p1.y-p[i].y)&&p1.x>p[i].x)) p1=p[k=i]; p2.x/=n,p2.y/=n; p[k]=p[0],p[0]=p1; qsort(p+1,n-1,sizeof(point),graham_cp); for (ch[0]=p[0],ch[1]=p[1],ch[2]=p[2],s=i=3;i<n;ch[s++]=p[i++]) for (;s>2&&xmult(ch[s-2],p[i],ch[s-1])<-eps;s--);}//鏋勯犲嚫鍖呮帴鍙ｅ嚱鏁?浼犲叆鍘熷鐐歸泦澶у皬n,鐐歸泦p(p鍘熸湁欏哄簭琚墦涔?)//榪斿洖鍑稿寘澶у皬,鍑稿寘鐨勭偣鍦╟onvex涓?br>//鍙傛暟maxsize涓?鍖呭惈鍏辯嚎鐐?涓?涓嶅寘鍚叡綰跨偣,緙虹渷涓?//鍙傛暟clockwise涓?欏烘椂閽堟瀯閫?涓?閫嗘椂閽堟瀯閫?緙虹渷涓?//鍦ㄨ緭鍏ヤ粎鏈夎嫢騫插叡綰跨偣鏃剁畻娉曚笉紼沖畾,鍙兘鏈夋綾繪儏鍐佃鍙﹁澶勭悊!//涓嶈兘鍘繪帀鐐歸泦涓噸鍚堢殑鐐?/span>int graham(int n,point* p,point* convex,int maxsize=1,int dir=1){ point* temp=new point[n]; int s,i; _graham(n,p,s,temp); for (convex[0]=temp[0],n=1,i=(dir?1:(s-1));dir?(i<s):i;i+=(dir?1:-1)) if (maxsize||!zero(xmult(temp[i-1],temp[i],temp[(i+1)%s]))) convex[n++]=temp[i]; delete []temp; return n;}int main(){ int n,m;//m鍑稿寘欏剁偣 double a,b; //memset() scanf("%d",&n); 
for(int i=0;i<n;i++){ scanf("%lf %lf",&p5[i].x,&p5[i].y);
} double maxn=0; m=graham(n,p5,convex1,1,1); for(int i=0;i<m;i++) for(int j=0;j<m;j++){ double tmp=dist(convex1[i],convex1[j]); if(maxn<tmp)maxn=tmp; } printf("%d\n",(int)maxn); //system("pause"); return 0; }]]>