[APIO2014]回文串

\(\text{Code}\)

#include<cstdio>
#include<cstring>
#include<iostream>
#define LL long long
#define re register
using namespace std;

const int N = 3e5 + 5;
char str[N];

struct PAM{
	int size, last, tot, tr[N][26], cnt[N], fail[N], len[N];
	char s[N];
	inline int Node(int l) 
	{
		++size;
		for(re int i = 0; i < 26; i++) tr[size][i] = 0;
		len[size] = l, fail[size] = cnt[size] = 0;
		return size;
	}
	inline void clear()
	{
		size = -1, s[last = tot = 0] = '$';
		Node(0), Node(-1), fail[0] = 1;
	}
	inline int getfail(int x)
	{
		while (s[tot - len[x] - 1] != s[tot]) x = fail[x];
		return x;
	}
	inline void insert(int x)
	{
		s[++tot] = str[x];
		int u = getfail(last), ch = str[x] - 'a';
		if (!tr[u][ch])
		{
			int v = Node(len[u] + 2);
			fail[v] = tr[getfail(fail[u])][ch], tr[u][ch] = v;
		}
		++cnt[last = tr[u][ch]];
	}
	inline LL query()
	{
		for(re int i = size; i >= 0; i--) cnt[fail[i]] += cnt[i];
		LL ans = 0;
		for(re int i = 1; i <= size; i++) ans = max(ans, 1LL * cnt[i] * len[i]);
		return ans;
	}
}P;

int main()
{
	P.clear();
	scanf("%s", str);
	int len = strlen(str);
	for(re int i = 0; i < len; i++) P.insert(i);
	printf("%lld\n", P.query());
}