【HDOJ2196】Computer（树的直径，树形DP）

 1 var f,g:array[1..21000,1..2]of longint;
 2     head,vet,next,len:array[1..21000]of longint;
 3     n,x,y,i,tot:longint;
 4 
 5 procedure add(a,b,c:longint);
 6 begin
 7  inc(tot);
 8  next[tot]:=head[a];
 9  vet[tot]:=b;
10  len[tot]:=c;
11  head[a]:=tot;
12 end;
13 
14 procedure dfs(u,fa:longint);
15 var e,v,t:longint;
16 begin
17  e:=head[u];
18  while e<>0 do
19  begin
20   v:=vet[e];
21   if v<>fa then
22   begin
23    dfs(v,u);
24    t:=f[v,1]+len[e];
25    if t>f[u,1] then
26    begin
27     f[u,2]:=f[u,1]; g[u,2]:=g[u,1];
28     f[u,1]:=t; g[u,1]:=v;
29    end
30     else if t>f[u,2] then
31     begin
32      f[u,2]:=t; g[u,2]:=v;
33     end;
34   end;
35   e:=next[e];
36  end;
37 end;
38 
39 procedure dfs2(u,fa:longint);
40 var e,v,t:longint;
41 begin
42  e:=head[u];
43  while e<>0 do
44  begin
45   v:=vet[e];
46   if v<>fa then
47   begin
48    t:=f[u,1]+len[e];
49    if v=g[u,1] then t:=f[u,2]+len[e];
50    if t>f[v,1] then
51    begin
52     f[v,2]:=f[v,1]; g[v,2]:=g[v,1];
53     f[v,1]:=t; g[v,1]:=u;
54    end
55     else if t>f[v,2] then
56     begin
57      f[v,2]:=t; g[v,2]:=u;
58     end;
59    dfs2(v,u);
60   end;
61   e:=next[e];
62  end;
63 end;
64 
65 begin
66  assign(input,‘2196.in‘); reset(input);
67  assign(output,‘2196.out‘); rewrite(output);
68  while not eof do
69  begin
70   fillchar(head,sizeof(head),0);
71   tot:=0;
72   fillchar(f,sizeof(f),0);
73   fillchar(g,sizeof(g),0);
74   read(n);
75   if n=0 then break;
76   for i:=2 to n do
77   begin
78    read(x,y);
79    add(i,x,y);
80    add(x,i,y);
81   end;
82   dfs(1,-1);
83   dfs2(1,-1);
84   for i:=1 to n do writeln(f[i,1]);
85  end;
86  close(input);
87  close(output);
88 end.