poj2014 不带修改区间第k大树

主席树 又称函数式线段树，又称可持久化线段树……缺点是内存有点儿大……

 type node1=record
      l,r,sum:longint;
      end;
      node2=record
      x,idx:longint;
      end;
 var q,i,j,k,tot,n,m:longint;
     a:array[..] of node2;
     rank,root:array[..] of longint;
     t:array[..] of node1;
 procedure qsort(h,l:longint);
  var i,j,m:longint;
      temp:node2;
  begin
  i:=h;j:=l;m:=a[(i+j)>>].x;
  repeat
   while a[i].x<m do inc(i);
   while a[j].x>m do dec(j);
   if i<=j then
    begin
    temp:=a[i];a[i]:=a[j];a[j]:=temp;
    inc(i);dec(j);
    end;
  until i>j;
  if i<l then qsort(i,l);
  if j>h then qsort(h,j);
  end;
 procedure insert(var x:longint;num,l,r:longint);
  var mid:longint;
  begin
  t[tot]:=t[x];
  x:=tot;
  inc(tot);
  inc(t[x].sum);
  if l=r then exit;
  mid:=(l+r)>>;
  if num<=mid then insert(t[x].l,num,l,mid)
  else insert(t[x].r,num,mid+,r);
  end;
 function query(i,j,k,l,r:longint):longint;
  var mid,tmp:longint;
  begin
  if l=r then exit(l);
  tmp:=t[t[j].l].sum-t[t[i].l].sum;
  mid:=(l+r)>>;
  if k<=tmp then exit(query(t[i].l,t[j].l,k,l,mid))
  else exit(query(t[i].r,t[j].r,k-tmp,mid+,r));
  end;
 procedure main;
  begin
  t[].l:=;t[].r:=;t[].sum:=;root[]:=;
  readln(n,m);
  for i:= to n do begin read(a[i].x);a[i].idx:=i;end;
  qsort(,n);
  tot:=;
  for i:= to n do rank[a[i].idx]:=i;
  for i:= to n do
   begin
   root[i]:=root[i-];
   insert(root[i],rank[i],,n);
   end;
  for q:= to m do
   begin
   readln(i,j,k);
   writeln(a[query(root[i-],root[j],k,,n)].x);
   end;
  end;
 begin
  main;
 end.