【ZJOI2017 Round1练习&UVA1057】D6T1 Routing（DP，SPFA）

题意：给你一个有向图， 并指定起点和终点。

问要从起点走向终点， 再从终点走向起点， 最少需要走过多少不同的节点。

对于 100%的数据， 有 N<=100， M<=min(1000,N*N)。 图中可能有重边或者自环

思路：

 const oo=;
 var head1,head2,vet1,vet2,next1,next2:array[..]of longint;
     q:array[..]of record
                           x,y:longint;
                          end;
     dis,f:array[..,..]of longint;
     inq:array[..,..]of boolean;
     n,m,i,j,k,cas,tot1,tot2,x,y,z:longint;

 function min(x,y:longint):longint;
 begin
  if x<y then exit(x);
  exit(y);
 end;

 procedure spfa;
 var i,j,u1,u2,e1,e2,v1,v2,t,w,t1,w1,tmp:longint;
 begin
  for i:= to n do
   for j:= to n do
   begin
    inq[i,j]:=false;
    dis[i,j]:=oo;
   end;
  t:=; w:=; t1:=; w1:=;
  q[].x:=; q[].y:=; inq[,]:=true; dis[,]:=;
  while t<w do
  begin
   inc(t); inc(t1);
   if t1=(n*n)<< then t1:=;
   u1:=q[t1].x; u2:=q[t1].y; inq[u1,u2]:=false;

   e1:=head1[u1];
   while e1<> do
   begin
    v1:=vet1[e1];
    tmp:=dis[u1,u2];
    if v1<>u2 then inc(tmp);
    if tmp<dis[v1,u2] then
    begin
     dis[v1,u2]:=tmp;
     if not inq[v1,u2] then
     begin
      inc(w); inc(w1);
      if w1=(n*n)<< then w1:=;
      q[w1].x:=v1; q[w1].y:=u2; inq[v1,u2]:=true;
     end;
    end;
    e1:=next1[e1];
   end;

   e2:=head2[u2];
   while e2<> do
   begin
    v2:=vet2[e2];
    tmp:=dis[u1,u2];
    if v2<>u1 then inc(tmp);
    if tmp<dis[u1,v2] then
    begin
     dis[u1,v2]:=tmp;
     if not inq[u1,v2] then
     begin
      inc(w); inc(w1);
      if w1=(n*n)<< then w1:=;
      q[w1].x:=u1; q[w1].y:=v2; inq[u1,v2]:=true;
     end;
    end;
    e2:=next2[e2];
   end;

   if (u1<>u2)and(dis[u1,u2]+f[u1,u2]-<dis[u2,u1]) then
   begin
    dis[u2,u1]:=dis[u1,u2]+f[u1,u2]-;
    if not inq[u2,u1] then
    begin
     inc(w); inc(w1);
     if w1=(n*n)<< then w1:=;
     q[w1].x:=u2; q[w1].y:=u1; inq[u2,u1]:=true;
    end;
   end;
  end;
 end;

 procedure add1(a,b:longint);
 begin
  inc(tot1);
  next1[tot1]:=head1[a];
  vet1[tot1]:=b;
  head1[a]:=tot1;
 end;

 procedure add2(a,b:longint);
 begin
  inc(tot2);
  next2[tot2]:=head2[a];
  vet2[tot2]:=b;
  head2[a]:=tot2;
 end;

 begin
  assign(input,'uva1057.in'); reset(input);
  assign(output,'uva1057.out'); rewrite(output);
  while not eof do
  begin
   read(n,m);
   if n= then break;
   for i:= to n do
   begin
    head1[i]:=;
    head2[i]:=;
   end;
   tot1:=; tot2:=;
   inc(cas);
   writeln('Network ',cas);
   for i:= to n do
    for j:= to n do
     if i<>j then f[i,j]:=oo;
   for i:= to m do
   begin
    read(x,y);
    f[x,y]:=;
    add1(x,y);
    add2(y,x);
   end;
   for i:= to n do
    for j:= to n do
     for k:= to n do f[j,k]:=min(f[j,k],f[j,i]+f[i,k]);
   if (f[,]=oo)or(f[,]=oo) then
   begin
    writeln('Impossible');
    writeln;
    continue;
   end;
   spfa;
   writeln('Minimum number of nodes = ',dis[,]);
   writeln;
  end;
  close(input);
  close(output);
 end.