hdu1392——凸包模板

http://acm.hdu.edu.cn/showproblem.php?pid=1392

type point=record      x,y:longint;     end;var s,p:array[1..200]of point;    n,l,i,min,i1,x1,tot:longint;    x,y:array[1..200]of longint;    p0:point;    ans:real; {operator -(a,b:point)c:point;begin c.x:=a.x-b.x; c.y:=a.y-b.y;end;operator *(a,b:point)c:longint;begin c:=a.x*b.y-a.y*b.x;end;       }function f(a,b,c:point):longint;var u1,u2,v1,v2:longint;begin u1:=a.x-c.x; v1:=a.y-c.y; u2:=b.x-c.x; v2:=b.y-c.y; f:=u1*v2-u2*v1;end;procedure qsort(l,r:longint;p0:point);var i,j:longint;    mid,t:point;begin i:=l;j:=r; mid:=p[(l+r) div 2]; repeat  while f(p[i],mid,p0)>0 do i:=i+1;  while f(p[j],mid,p0)<0 do j:=j-1;  if i<=j then   begin    t:=p[i];p[i]:=p[j];p[j]:=t;    i:=i+1;j:=j-1;   end; until i>j; if i<r then qsort(i,r,p0); if l<j then qsort(l,j,p0);end;begin read(n); while n<>0 do  begin   min:=maxlongint;x1:=0;i1:=0;   for i:=1 to n do    begin     read(x[i],y[i]);     if (min=y[i])and(x1>x[i]) then begin x1:=x[i];i1:=i;end;     if min>y[i] then begin min:=y[i];x1:=x[i];i1:=i;end;    end;   p0.x:=x1;p0.y:=min;   l:=0;   for i:=1 to n do    if i<>i1 then    begin     l:=l+1;     p[l].x:=x[i];     p[l].y:=y[i];    end;   qsort(1,n-1,p0);   fillchar(s,sizeof(s),0);   tot:=1;   s[1]:=p0;   for i:=1 to n-1 do    begin     while (tot>=2)and(f(s[tot-1],p[i],s[tot])>0) do tot:=tot-1;     tot:=tot+1;     s[tot]:=p[i];    end;   ans:=0;   for i:=1 to tot-1 do    ans:=ans+sqrt(sqr(s[i].x-s[i+1].x)+sqr(s[i].y-s[i+1].y));   if tot>2 then ans:=ans+sqrt(sqr(s[tot].x-s[1].x)+sqr(s[tot].y-s[1].y));   writeln(ans:0:2);   read(n);  end;end.