找第k大的数（解法3：快速排序）

var i,k,n:longint;
    a:array[1..100000]of longint;

procedure qsort(l,r:longint);
var i,j,m,t:longint;
begin
  if l=r then exit;
  i:=l; j:=r; m:=a[k];
  repeat
    while a[i]<m do inc(i);
    while a[j]>m do dec(j);
    if i<j then
    begin
      t:=a[i]; a[i]:=a[j]; a[j]:=t;
      inc(i); dec(j);
    end;
  until i>=j;
  if i=k then exit;
  if i>k then qsort(l,j) else qsort(j+1,r);
end;

begin
  assign(input,'maxk.in'); reset(input);
  assign(output,'maxk.out'); rewrite(output);
  read(n,k);
  for i:=1 to n do read(a[i]);
  qsort(1,n);
  writeln(a[k]);
  close(input); close(output);
end.