【APIO2014】Palindromes

2014年好像没有回文树， 但是回文树出来之后就变成裸题了

#include <algorithm>
#include <cstring>
#include <cstdio>
#include <iostream>

#define rep(i, s, t) for(int i = (s), i##E = (t); i <= i##E; ++i)
#define dec(i, s, t) for(int i = (s), i##E = (t); i >= i##E; --i)

using namespace std;

const int SIGMA = 26;
const int MX_N = (3e5 + 10) * 2;

char s[MX_N];

namespace PAM {
    int lst, tot;
    int len[MX_N], val[MX_N];
    int fail[MX_N], ch[MX_N][SIGMA];

    void init() {
        tot = 1;
        fail[0] = fail[1] = 1;
        len[1] = -1, lst = 0;
    }

    void solve() {
        init();
        rep(i, 1, strlen(s + 1)) {
            int x = s[i] - 'a', h = lst, u = 0;
            while(s[i-len[h]-1] != s[i]) h = fail[h];
            if(!ch[h][x]) {
                len[u=++tot] = len[h] + 2;
                int v = fail[h];
                while(s[i-len[v]-1] != s[i]) v = fail[v];
                fail[u] = ch[v][x], ch[h][x] = u;
            }++val[lst = ch[h][x]];
        }
    }
}using namespace PAM;

long long count() {
    long long ret = 0;
    dec(i, tot, 2) val[fail[i]] += val[i];
    rep(i, 2, tot) ret = max(ret, (long long)val[i] * len[i]);
    return ret;
}

int main() {
#ifndef ONLINE_JUDGE
    freopen("input.in", "r", stdin);
    freopen("res.out", "w", stdout);
#endif
    scanf("%s", s + 1);
    solve();
    printf("%lld
", count());
    return 0;
}