凸包模板题

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http://acm.nyist.net/JudgeOnline/problemrank.php?pid=78

AC代码：

#include<iostream>#include<algorithm>#include<cstdio>#include<string>#include<cstring>#define N 105using namespace std;struct Point{int x;int y;}p[N];int top,n,s[N];int dis(const Point& a,const Point& b){return (a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y);}int cross(const Point& a,const Point& b,const Point& c){return (b.x-a.x)*(c.y-a.y)-(c.x-a.x)*(b.y-a.y);}bool cmp(const Point& a,const Point& b)//幅角排序{int ans=cross(p[0],a,b);if((ans>0)||(ans==0&&dis(p[0],a)>dis(p[0],b))) return true;return false;}bool cmp1(const Point& a,const Point& b){return (a.x<b.x||(a.x==b.x&&a.y<b.y));} void graham()//凸包模板 { s[0]=0; s[1]=1; top=1; for(int i=2;i!=n;++i) { while(top&&cross(p[s[top-1]],p[s[top]],p[i])<0) top--; s[++top]=i; } top++; } int main() { int T; scanf("%d",&T); while(T--) { scanf("%d",&n); for(int i=0;i!=n;++i) scanf("%d%d",&p[i].x,&p[i].y);  Point ans=p[0];  int u=0;  for(int i=1;i!=n;++i)  if((ans.y>p[i].y)||(ans.y==p[i].y&&ans.x>p[i].x)) ans=p[i],u=i;  if(u) swap(p[u],p[0]);   sort(p+1,p+n,cmp);   memset(s,0,sizeof(s));   graham();   Point result[N];   for(int i=0;i!=top;++i)   result[i]=p[s[i]];   sort(result,result+top,cmp1);   for(int i=0;i!=top;++i)   cout<<result[i].x<<" "<<result[i].y<<endl;   }return 0; }