花帝香精:TJU1082？

给你maigo的程序,自己看吧
program tju1082;
const
maxn=30000;
zero=1e-6;
type
dot=record x,y:longint;end;
var
d:array[1..maxn]of dot;
n,i,j,l,m:longint;
td:dot;
ans:extended;
function cross(a,b,c,d:dot):shortint;
var
x1,x2,y1,y2:extended;
begin
x1:=b.x*1.0-a.x;y1:=b.y*1.0-a.y;
x2:=d.x*1.0-c.x;y2:=d.y*1.0-c.y;
x1:=x1*y2-x2*y1;
if abs(x1)<zero then
cross:=0
else if x1>0 then
cross:=1
else
cross:=-1;
end;
procedure qsort(s,t:word);
var
p,i,j:word;
td:dot;
begin
if s>=t then exit;
p:=s+random(t-s+1);
td:=d[p];d[p]:=d[s];
i:=s;j:=t;
repeat
while (i<j) and (cross(d[1],d[j],d[1],td)<=0) do dec(j);
if i=j then break;d[i]:=d[j];inc(i);
while (i<j) and (cross(d[1],d[i],d[1],td)>=0) do inc(i);
if i=j then break;d[j]:=d[i];dec(j);
until i=j;
d[i]:=td;
qsort(s,i-1);
qsort(i+1,t);
end;
function next(x:word):word;
begin
if x=l then next:=1 else next:=x+1;
end;
procedure update(a,b:integer);
var
dist:real;
begin
dist:=sqr(d[a].x*1.0-d[b].x)+sqr(d[a].y*1.0-d[b].y);
if dist>ans then ans:=dist;
end;
begin
repeat
read(n);
if n<2 then begin
if n=1 then read(j,j);
writeln('0.00');
continue;
end
else if n=2 then begin
read(i,j,l,m);
writeln(sqrt(sqr(i*1.0-l)+sqr(j*1.0-m)):0:2);
continue;
end;

for i:=1 to n do begin
read(d[i].x,d[i].y);
if (d[i].y<d[1].y) or (d[i].y=d[1].y) and (d[i].x<d[1].x) then begin
td:=d[1];d[1]:=d[i];d[i]:=td;
end;
end;

qsort(2,n);

j:=2;
for i:=3 to n do
if cross(d[1],d[j],d[1],d[i])>0 then
inc(j)
else if (d[i].y>d[j].y) or (d[i].y=d[j].y) and (d[i].x>d[j].x) then
d[j]:=d[i];
l:=2;
for i:=3 to j do begin
while cross(d[l-1],d[l],d[l-1],d[i])<=0 do dec(l);
inc(l);d[l]:=d[i];
end;

ans:=0;m:=3;
for i:=1 to l do begin
j:=next(i);
while cross(d[i],d[j],d[m],d[next(m)])>0 do begin
m:=next(m);
end;
update(i,m);update(j,m);
end;
writeln(sqrt(ans):0:2);
until seekeof;
end.