【HDOJ3068】最长回文（manacher）

题意：求一个由小写字母组成的字符串中的最长回文长度

cas<=120 n<=110000

思路：试manacher板子

var a:array[0..300000]of char;
    p:array[0..300000]of longint;
    ch:ansistring;
    len,n,i,mx,id,ans:longint;

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

function max(x,y:longint):longint;
begin
 if x>y then exit(x);
 exit(y);
end;

begin
 assign(input,'hdoj3068.in'); reset(input);
 assign(output,'hdoj3068.out'); rewrite(output);
 while not eof do
 begin
  readln(ch);
  len:=length(ch);
  if len=0 then continue;
  n:=2; a[1]:='@'; a[2]:='#';
  for i:=1 to len do
  begin
   inc(n); a[n]:=ch[i];
   inc(n); a[n]:='#';
  end;
  inc(n); a[n]:='$';
  mx:=0; id:=0;
  for i:=2 to n-1 do
  begin
   if mx>i then p[i]:=min(p[2*id-i],mx-i)
    else p[i]:=1;
   while a[i+p[i]]=a[i-p[i]] do inc(p[i]);
   if p[i]+i>mx then
   begin
    mx:=p[i]+i;
    id:=i;
   end;
  end;
  ans:=1;
  for i:=2 to n-1 do ans:=max(ans,p[i]-1);
  writeln(ans);
 end;
 close(input);
 close(output);
end.