【Tsinsen】A1280. 最长双回文串
http://www.tsinsen.com/A1280###
题目分析:记录一个点向后和向前的最长回文串,然后就是max(Llen[i]+Rlen[i+1])了。
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std ;
typedef long long LL ;
#define rep( i , a , b ) for ( int i = ( a ) ; i < ( b ) ; ++ i )
#define For( i , a , b ) for ( int i = ( a ) ; i <= ( b ) ; ++ i )
#define rev( i , a , b ) for ( int i = ( a ) ; i >= ( b ) ; -- i )
#define clr( a , x ) memset ( a , x , sizeof a )
const int MAXN = 100005 ;
const int N = 26 ;
struct Palindromic_Tree {
int next[MAXN][N] ;
int fail[MAXN] ;
int cnt[MAXN] ;
int len[MAXN] ;
int S[MAXN] ;
int last ;
int n ;
int p ;
int newnode ( int l ) {
for ( int i = 0 ; i < N ; ++ i ) next[p][i] = 0 ;
cnt[p] = 0 ;
len[p] = l ;
return p ++ ;
}
void init () {
p = 0 ;
newnode ( 0 ) ;
newnode ( -1 ) ;
last = 0 ;
n = 0 ;
S[n] = -1 ;
fail[0] = 1 ;
}
int get_fail ( int x ) {
while ( S[n - len[x] - 1] != S[n] ) x = fail[x] ;
return x ;
}
int add ( int c ) {
c -= 'a' ;
S[++ n] = c ;
int cur = get_fail ( last ) ;
if ( !next[cur][c] ) {
int now = newnode ( len[cur] + 2 ) ;
fail[now] = next[get_fail ( fail[cur] )][c] ;
next[cur][c] = now ;
}
last = next[cur][c] ;
cnt[last] ++ ;
return len[last] ;
}
void count () {
for ( int i = p - 1 ; i >= 0 ; -- i ) cnt[fail[i]] += cnt[i] ;
}
} ;
Palindromic_Tree T ;
int n ;
int len[MAXN] ;
char s[MAXN] ;
void solve () {
int ans = 0 ;
n = strlen ( s ) ;
T.init () ;
for ( int i = n - 1 ; i >= 0 ; -- i ) {
len[i] = T.add ( s[i] ) ;
}
T.init () ;
for ( int i = 0 ; i < n - 1 ; ++ i ) {
ans = max ( ans , T.add ( s[i] ) + len[i + 1] ) ;
}
printf ( "%d\n" , ans ) ;
}
int main () {
while ( ~scanf ( "%s" , s ) ) solve () ;
return 0 ;
}