先上我原来的错误的代码

type  node=^link;  link=record    num:int64;    next:node;  end;var fa:array[0..300000,0..100] of int64; dep:array[0..300000] of int64;   nd:array[0..300000] of node;  b:array[0..300000] of boolean;  dl:array[0..300000] of int64; n,m,maxdep,ans,t1,t2:int64; i:longint; procedure maketree; var  t1,t2,head,tail:int64;  i,j:longint;  p:node;   begin         for i:=0 to n do       b[i]:=false;     for i:=1 to n-1 do       begin         read(t1,t2);                    new(p);         p^.num:=t2;p^.next:=nd[t1];nd[t1]:=p;         new(p);         p^.num:=t1;p^.next:=nd[t2];nd[t2]:=p;       end;      new(p);      head:=1;tail:=1;dl[head]:=1;b[1]:=true;       while head<=tail do         begin           p:=nd[dl[head]];           while p<>nil do             begin               if b[p^.num]=false then                 begin                   inc(tail);                   dl[tail]:=p^.num;                   fa[p^.num,0]:=dl[head];                   dep[p^.num]:=dep[dl[head]]+1;                   b[p^.num]:=true;                   if dep[p^.num]>maxdep then maxdep:=dep[p^.num];                 end;               p:=p^.next;             end;           inc(head);         end;      for j:=1 to trunc(ln(maxdep)/ln(2))+1 do        for i:=0 to n do          if dep[i]>=1<
     
      dep[b] then        begin          t:=a;          a:=b;          b:=t;        end;      if dep[a]<>dep[b] then        for i:=trunc(ln(dep[b]-dep[a])/ln(2)) downto 0 do          if dep[b]-1<
      =dep[a] then            begin               b:=fa[b,i];               ans:=ans+1<
       
        b then      for i:=trunc(ln(dep[a])/ln(2)) downto 0 do        if fa[a,i]<>fa[b,i] then          begin            a:=fa[a,i];            b:=fa[b,i];            ans:=ans+1<<(i+1);          end;      if a<>b then inc(ans,2);    end;  begin      readln(n);    if n=1 then      begin        writeln(0);        halt;       end;    maketree;    readln(m);    read(t1);    for i:=2 to m do      begin        read(t2);             lca(t1,t2);        t1:=t2;      end;    writeln(ans);      end.
       
     

这个写法WA了一个点，答案比标准答案大。

最后发现可能是ln出现了误差，导致结果偏小，使两点无法移到同层。在后面的移动中无论怎样都无法移到同点，使答案比原来大二

 

改正后的模板

type  node=^link;  link=record    num:int64;    next:node;  end;var fa:array[0..300000,0..100] of int64; dep:array[0..300000] of int64;   nd:array[0..300000] of node;  b:array[0..300000] of boolean;  dl:array[0..300000] of int64;  n,m,maxdep,ans,t1,t2:int64;  i:longint; procedure maketree; var  t1,t2,head,tail:int64;  i,j:longint;  p:node;   begin         for i:=0 to n do       b[i]:=false;     for i:=1 to n-1 do       begin         read(t1,t2);                    new(p);         p^.num:=t2;p^.next:=nd[t1];nd[t1]:=p;         new(p);         p^.num:=t1;p^.next:=nd[t2];nd[t2]:=p;       end;      new(p);      head:=1;tail:=1;dl[head]:=1;b[1]:=true;       while head<=tail do         begin           p:=nd[dl[head]];           while p<>nil do             begin               if b[p^.num]=false then                 begin                   inc(tail);                   dl[tail]:=p^.num;                   fa[p^.num,0]:=dl[head];                   dep[p^.num]:=dep[dl[head]]+1;                   b[p^.num]:=true;                   if dep[p^.num]>maxdep then maxdep:=dep[p^.num];                 end;               p:=p^.next;             end;           inc(head);         end;      for j:=1 to trunc(ln(maxdep)/ln(2))+1 do        for i:=0 to n do          if dep[i]>=1<
     
      dep[b] then        begin          t:=a;          a:=b;          b:=t;        end;      if dep[a]<>dep[b] then        for i:=trunc(ln(dep[b]-dep[a])/ln(2))+10 downto 0 do          if dep[b]-1<
      =dep[a] then            begin               b:=fa[b,i];               ans:=ans+1<
       
        b then      for i:=trunc(ln(dep[a])/ln(2))+10 downto 0 do        if fa[a,i]<>fa[b,i] then          begin            a:=fa[a,i];            b:=fa[b,i];            ans:=ans+1<<(i+1);          end;      if a<>b then inc(ans,2);    end;  begin      readln(n);    if n=1 then      begin        writeln(0);        halt;       end;    maketree;    readln(m);    read(t1);    for i:=2 to m do      begin        read(t2);             lca(t1,t2);        t1:=t2;      end;    writeln(ans);      end.