POJ1113 (Pascal)

poj1113.pas

const
  zero=1e-6;

var
  n:longint;
  x,y:array [0..10000] of longint;

function cross(a,b,c:longint):longint; inline;
begin
  exit((x[b]-x[a])*(y[c]-y[a])-(x[c]-x[a])*(y[b]-y[a]));
end;

function sgn(k:double):longint; inline;
begin
  if abs(k)<zero then exit(0);
  if k>0 then exit(1) else exit(-1);
end;

function dis(p,q:longint):int64; inline;
begin
  exit(sqr(x[q]-x[p])+sqr(y[q]-y[p]));
end;

function cmp(a,b,c:longint):boolean;
var
  t:longint;

begin
  t:=sgn(cross(a,b,c));
  cmp:=false;
  if t>0 then exit(true);
  if t=0 then
    if dis(a,c)>dis(a,b) then exit(true);
end;

procedure main;
var
  i,j,l:longint;
  p,q,m:longint;
  hull:array [0..10000] of longint;
  s:double;

begin
  readln(n,l);
  p:=1;
  for i:=1 to n do
    begin
      readln(x[i],y[i]);
      if (x[i]<x[p]) or ((x[i]=x[p]) and (y[i]<y[p])) then p:=i;
    end;
  m:=0;
  fillchar(hull,sizeof(hull),0);
  repeat
    q:=0;
    inc(m);
    hull[m]:=p;
    for i:=1 to n do
      if (i<>p) and ((q=0) or (cmp(p,q,i))) then
        q:=i;
    if q=hull[1] then break;
    p:=q;
  until false;
  s:=sqrt(dis(hull[m],hull[1]));
  for i:=1 to m-1 do s:=s+sqrt(dis(hull[i],hull[i+1]));
  s:=s+2*pi*l;
  writeln(round(s));
end;

begin
  main;
end.