[BZOJ1776] [Usaco2010 Hol]cowpol 奶牛政坛

传送门

题目大意

题解

var
st:array[0..200005,0..30]of longint;
w,u:array[0..600005,1..2]of longint;
t,dep:array[0..200005]of longint;
i,j,k:longint;
n,m,len1,len2,head,tail,tt,v,a,b,root,ans,maxd:longint;
procedure init1(a,b:longint);
begin
w[len1,1]:=b;
if w[a,2]=0
then w[a,2]:=len1 else w[w[a,1],2]:=len1;
w[a,1]:=len1; inc(len1);
end;

procedure init2(a,b:longint);
begin
u[len2,1]:=b;
if u[a,2]=0
then u[a,2]:=len2 else u[u[a,1],2]:=len2;
u[a,1]:=len2; inc(len2);
end;

function lca(a,b:longint):longint;
var i:longint;
begin
if dep[a]>dep[b] then begin i:=a; a:=b; b:=i; end;
for i:=trunc(ln(maxd)/ln(2)) downto 0 do
if dep[st[b,i]]>=dep[a] then b:=st[b,i];
if a=b then exit(a);
for i:=trunc(ln(maxd)/ln(2)) downto 0 do
if st[a,i]<>st[b,i]
then begin a:=st[a,i]; b:=st[b,i]; end;
exit(st[a,0]);
end;

begin
readln(n,m); len1:=n+1; len2:=m+1;
for i:=1 to n do
begin
readln(a,b);
if b=0 then root:=i;
init1(b,i); st[i,0]:=b; init2(a,i);
end;
dep[root]:=1; t[1]:=root; head:=1; tail:=2; maxd:=1;
while head<tail do
begin
v:=t[head]; inc(head); tt:=w[v,2];
while tt<>0 do
begin
dep[w[tt,1]]:=dep[v]+1;
if dep[v]+1>maxd then maxd:=dep[v]+1;
t[tail]:=w[tt,1]; inc(tail);
tt:=w[tt,2];
end;
end;
for j:=1 to trunc(ln(maxd)/ln(2)) do
for i:=1 to n do
st[i,j]:=st[st[i,j-1],j-1];
dep[0]:=0;
for i:=1 to m do
begin
tt:=u[i,2]; k:=0;
while tt<>0 do
begin
if dep[u[tt,1]]>dep[k]
then k:=u[tt,1];
tt:=u[tt,2];
end;
tt:=u[i,2]; ans:=0;
while tt<>0 do
begin
j:=lca(k,u[tt,1]);
if dep[k]+dep[u[tt,1]]-2*dep[j]>ans
then ans:=dep[k]+dep[u[tt,1]]-2*dep[j];
tt:=u[tt,2];
end;
writeln(ans);
end;
end.