poj1655 Balancing Act求树的重心

 1 program rrr(input,output);
 2 type
 3   etype=record
 4      t,next:longint;
 5   end;
 6 var
 7   e:array[0..40040]of etype;
 8   a,q,father,siz,f:array[0..20020]of longint;
 9   v:array[0..20020]of boolean;
10   tt,i,j,n,x,y,cnt,h,t,ans,min:longint;
11 function max(a,b:longint):longint;
12 begin
13    if a>b then exit(a) else exit(b);
14 end;
15 procedure add(x,y:longint);
16 begin
17    inc(cnt);e[cnt].t:=y;e[cnt].next:=a[x];a[x]:=cnt;
18 end;
19 begin
20    assign(input,‘r.in‘);assign(output,‘r.out‘);reset(input);rewrite(output);
21    readln(tt);
22    for i:=1 to tt do
23       begin
24          readln(n);
25          for j:=1 to n do a[j]:=0;cnt:=0;
26          for j:=1 to n-1 do begin read(x,y);add(x,y);add(y,x); end;
27          fillchar(v,sizeof(v),false);
28          h:=0;t:=1;q[1]:=1;v[1]:=true;
29          while h<t do
30             begin
31                inc(h);
32                j:=a[q[h]];
33                while j<>0 do
34                   begin
35                      if not v[e[j].t] then
36                         begin
37                            v[e[j].t]:=true;father[e[j].t]:=q[h];
38                            inc(t);q[t]:=e[j].t;
39                         end;
40                      j:=e[j].next;
41                   end;
42             end;
43          for j:=1 to n do siz[j]:=1;
44          fillchar(f,sizeof(f),0);min:=n;
45          for j:=n downto 2 do
46             begin
47                t:=max(f[q[j]],n-siz[q[j]]);
48                if (t<min) or (t=min) and (q[j]<ans) then begin ans:=q[j];min:=t; end;
49                inc(siz[father[q[j]]],siz[q[j]]);
50                if siz[q[j]]>f[father[q[j]]] then f[father[q[j]]]:=siz[q[j]];
51             end;
52          if f[1]<=min then begin ans:=1;min:=f[1]; end;
53          writeln(ans,‘ ‘,min);
54       end;
55    close(input);close(output);
56 end.