SPFA为啥会超时啊!

program P3509;
var p,q,i,j,t,last,k,h,n:longint;
    go,back:array[0..1900001,1..4] of longint;
    g1,g2,dui:array[0..1900001] of longint;
    dist:array[0..1900001] of int64;
    max:int64;
begin
  readln(n);
  for t:=1 to n do
    begin
      readln(p,q);
      fillchar(go,sizeof(go),0);
      fillchar(back,sizeof(back),0);
      fillchar(g1,sizeof(g1),0);
      fillchar(g2,sizeof(g2),0);
      for i:=1 to q do
        begin
          readln(go[i,1],go[i,2],go[i,3]);
          go[i,4]:=g1[go[i,1]];
          g1[go[i,1]]:=i;
          back[i,1]:=go[i,2];
          back[i,2]:=go[i,1];
          back[i,3]:=go[i,3];
          back[i,4]:=g2[back[i,1]];
          g2[back[i,1]]:=i;
        end;
      max:=0;
      for i:=1 to p do
        dist[i]:=maxlongint div 3;
      dist[1]:=0;
      dui[1]:=1;
      i:=1;j:=1;
      while i<=j do
        begin
          last:=j;
          for k:=i to last do
            begin
              h:=g1[dui[k]];
              while h<>0 do
                begin
                  if dist[dui[k]]+go[h,3]<dist[go[h,2]]
                    then begin
                           dist[go[h,2]]:=dist[dui[k]]+go[h,3];
                           inc(j);
                           dui[j]:=go[h,2];
                         end;
                  h:=go[h,4];
                end;
            end;
          i:=last+1;
        end;
      for i:=2 to p do
        begin
          max:=max+dist[i];
          //writeln(1,'to',i,'=',dist[i]);
        end;
      for i:=1 to p do
        dist[i]:=maxlongint div 3;
      dist[1]:=0;
      dui[1]:=1;
      i:=1;j:=1;
      while i<=j do
        begin
          last:=j;
          for k:=i to last do
            begin
              h:=g2[dui[k]];
              while h<>0 do
                begin
                  if dist[dui[k]]+back[h,3]<dist[back[h,2]]
                    then begin
                           dist[back[h,2]]:=dist[dui[k]]+back[h,3];
                           inc(j);
                           dui[j]:=back[h,2];
                         end;
                  h:=back[h,4];
                end;
            end;
          i:=last+1;
        end;
      for i:=2 to p do
        begin
          max:=max+dist[i];
        end;
      writeln(max);
    end;
end.
赤裸裸的spfa啊，是有什么地方没做好吗？