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[..] of node;
     s,c,p:array[..] of longint;
     i,n,m,block,l,r,k:longint;
     anss:int64;
 function gcd(x,y:longint):longint;
  begin
  if y= 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)>>];
   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:= to n do read(c[i]);
    block:=trunc(sqrt(n));
    for i:= to n do p[i]:=(i-) div block+;
    for i:= 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(,m);
   l:=;r:=;
   for i:= to m do
     begin
       while r<a[i].r do
         begin
          update(r+,);inc(r);
         end;
       while r>a[i].r do
         begin
          update(r,-);dec(r);
         end;
       while l<a[i].l do
         begin
         update(l,-);inc(l);
         end;
       while l>a[i].l do
         begin
         update(l-,);dec(l);
         end;
       if a[i].l=a[i].r then
         begin
          a[i].x:=;a[i].y:=;
          continue;
         end;
       with a[i] do
        begin
          x:=anss-(r-l+);
          y:=(r-l+)*(r-l);
          k:=gcd(x,y);
          x:=x div k;y:=y div k;
        end;
       end;
   for i:= to m do ans[a[i].id]:=a[i];
   for i:= to m do with ans[i] do writeln(x,'/',y);
   end;
 begin
   init;
   main;
 end.