2009国家集训队小Z的袜子

莫队算法？

感觉没什么优越性啊？难道就是因为在排序的时候cmp函数的不同？这样做为什么减少时限啊？

我带着疑惑敲了代码，却一直有bug……

代码：

type node=record
     l,r,id,x,y:int64;
     end;
var a,ans:array[1..55000] of node;
    s,c,p:array[1..55000] of longint;
    i,n,m,block,l,r,k:longint;
    anss:int64;
function gcd(x,y:longint):longint;
 begin
 if y=0 then exit(x) else exit(gcd(y,x mod y));
 end;
function cmp(x,y:node):boolean;
 begin
 if p[x.l]=p[y.l] then exit(x.r<y.r);
 exit(x.l<y.l);
 end;
procedure sort(h,l:longint);
 var i,j:longint;
     tmp,mm:node;
 begin
  i:=h;j:=l;mm:=a[(i+j)>>1];
  repeat
    while cmp(a[i],mm) do inc(i);
    while cmp(mm,a[j]) do dec(j);
    if i<=j then
      begin
       tmp:=a[i];a[i]:=a[j];a[j]:=tmp;
       inc(i);dec(j);
      end;
  until i>j ;
  if i<l then sort(i,l);
  if j>h then sort(h,j);
 end;
procedure init;
 begin
   readln(n,m);
   for i:=1 to n do read(c[i]);
   block:=trunc(sqrt(n));
   for i:=1 to n do p[i]:=(i-1) div block+1;
   for i:=1 to m do
    begin
      readln(a[i].l,a[i].r);
      a[i].id:=i;
    end;
 end;
procedure update(p,add:longint);
 begin
  dec(anss,sqr(s[c[p]]));
  inc(s[c[p]],add);
  inc(anss,sqr(s[c[p]]));
 end;
procedure main;
 begin
  sort(1,m);
  l:=1;r:=0;
  for i:=1 to m do
    begin
      while r<a[i].r do
        begin
         update(r+1,1);inc(r);
        end;
      while r>a[i].r do
        begin
         update(r,-1);dec(r);
        end;
      while l<a[i].l do
        begin
        update(l,-1);inc(l);
        end;
      while l>a[i].l do
        begin
        update(l-1,1);dec(l);
        end;
      if a[i].l=a[i].r then
        begin
         a[i].x:=0;a[i].y:=1;
         continue;
        end;
      with a[i] do
       begin
         x:=anss-(r-l+1);
         y:=(r-l+1)*(r-l);
         k:=gcd(x,y);
         x:=x div k;y:=y div k;
       end;
      end;
  for i:=1 to m do ans[a[i].id]:=a[i];
  for i:=1 to m do with ans[i] do writeln(x,'/',y);
  end;
begin
  init;
  main;
end.