Submission #1186115

#	Time	Username	Problem	Language	Result	Execution time	Memory
1186115		thieunguyenhuy	Palindromes (APIO14_palindrome)	C++20	0 / 100	0 ms	328 KiB

palindrome

#include <bits/stdc++.h>
using namespace std;

#define POPCOUNT(n) (__builtin_popcountll((n)))
#define CLZ(n) (__builtin_clzll((n)))
#define CTZ(n) (__builtin_ctzll((n)))
#define LOG(n) (63 - __builtin_clzll((n)))
#define BIT(n, i) (((n) >> (i)) & 1ll)
#define MASK(i) (1ll << (i))
#define FLIP(n, i) ((n) ^ (1ll << (i)))
#define ON(n, i) ((n) | MASK(i))
#define OFF(n, i) ((n) & ~MASK(i))

#define Int __int128
#define fi first
#define se second
#define hash pvhdeptrai
#define rank pvhkhongdeptrai

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;
typedef pair<long long, int> pli;
typedef pair<int, long long> pil;
typedef vector<pair<int, int>> vii;
typedef vector<pair<long long, long long>> vll;
typedef vector<pair<long long, int>> vli;
typedef vector<pair<int, long long>> vil;

template <class T1, class T2> bool maximize(T1 &x, T2 y) {
    if (x < y) {
        x = y;
        return true;
    }
    return false;
}
template <class T1, class T2> bool minimize(T1 &x, T2 y) {
    if (x > y) {
        x = y;
        return true;
    }
    return false;
}

template <class T> void remove_duplicate(vector<T> &ve) {
    sort (ve.begin(), ve.end());
    ve.resize(unique(ve.begin(), ve.end()) - ve.begin());
}

mt19937_64 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
template <class T1, class T2> T1 random(T1 l, T2 r) {
    return uniform_int_distribution<T1>(l, r)(rng);
}
template <class T> T random(T r) {
    return rng() % r;
}

const int N = 6e5 + 5, LG = 20;
const int MOD = 1e9 + 9;
const int inf = 1e9;
const long long INF = 1e18;

const int base = 311;

string s;
int sa[N], lcp[N], rank[N], w[N];
int pw[N], hash[N], rev_hash[N];
int rmq[N][LG];
pii pa[N];

struct SuffixArray {
	string str;
	int n;

	SuffixArray(string _s = "") {
		str = _s, n = str.size();
		get_sa(), get_lcp();
	}

	void get_sa() {
		for (int i = 0; i < n; ++i) {
			sa[i] = i;
			pa[i] = make_pair(int(str[i]), 0);
		}

		auto cmp = [&](int x, int y) {
			return pa[x] < pa[y];
		};

		sort (sa, sa + n, cmp);

		for (int len = 1; len <= n; len <<= 1) {
			int cnt = 0;
			for (int i = 0; i < n; ++i) {
				if (i > 0 && pa[sa[i - 1]] == pa[sa[i]]) w[sa[i]] = w[sa[i - 1]];
				else w[sa[i]] = ++cnt;
			}

			if (cnt == n) break;

			for (int i = 0; i < n; ++i) {
				pa[i] = make_pair(w[i], (i + len < n ? w[i + len] : 0));
			}

			sort (sa, sa + n, cmp);
		}
	}

	void get_lcp() {
		for (int i = 0; i < n; ++i) rank[sa[i]] = i;
		for (int i = 0, k = 0; i < n; lcp[rank[i++]] = k) {
			if (rank[i] > 0) {
				int j = sa[rank[i] - 1];
				if (k > 0) --k;
				while (str[i + k] == str[j + k]) ++k;
			}
			else k = 0;
		}
	}
};

int getHash(int l, int r) {
	return (0ll + hash[r] - 1ll * hash[l - 1] * pw[r - l + 1] + 1ll * MOD * MOD) % MOD;
}
int get_revHash(int l, int r) {
	return (0ll + rev_hash[l] - 1ll * rev_hash[r + 1] * pw[r - l + 1] + 1ll * MOD * MOD) % MOD;
}

bool isPalin(int l, int r) {
	return getHash(l, r) == get_revHash(l, r);
}

signed main() {
    ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);

    cin >> s;
    // s = string(3e5, 'a');

    string t(1, '#');
    for (int i = 0; i < s.size(); ++i) {
    	t += s[i];
    	t += '#';
    }

    // cerr << "t = " << t << '\n';
    
    int n = t.size(); SuffixArray T(t);

    for (int i = 0; i < n; ++i) rmq[i][0] = lcp[i];
    for (int i = 1; i < LG; ++i) for (int j = 0; j + MASK(i) - 1 < n; ++j) {
    	rmq[j][i] = min(rmq[j][i - 1], rmq[j + MASK(i - 1)][i - 1]);
    }

    auto get_lcp = [&](int l, int r) {
    	++l; int g = LOG(r - l + 1);
    	return min(rmq[l][g], rmq[r - MASK(g) + 1][g]);
    };

    pw[0] = 1;
    for (int i = 1; i <= n; ++i) pw[i] = 1ll * pw[i - 1] * base % MOD;

    hash[0] = t[0];
	for (int i = 1; i < n; ++i)
		hash[i] = (1ll * hash[i - 1] * base + t[i]) % MOD;
    for (int i = n - 1; i >= 0; --i)
    	rev_hash[i] = (1ll * rev_hash[i + 1] * base + t[i]) % MOD;

    // if (s.size() > 100000) assert(false);

    // int ahuhu = 0;

    ll ans = 0;
    for (int i = 0; i < n; ++i) {
    	int start_len = max(0, lcp[rank[i]] - 1);

    	auto work = [&](int len) {
    		int real_len = 2 * len + 1;
    		if (t[i] == '#') {
    			int x = (len / 2);
    			real_len -= 2 * x + 1;
    		}
    		else {
    			int x = (len + 1) / 2;
    			real_len -= 2 * x;
    		}

    		if (real_len == 0) return;

    		int p = rank[i - len];
    		int low = 0, high = p - 1, L = p, R = p;
    		while (low <= high) {
    			int mid = (low + high) >> 1;
    			if (get_lcp(mid, p) >= 2 * len + 1) high = (L = mid) - 1;
    			else low = mid + 1;
    		}

    		low = p + 1, high = n - 1;
    		while (low <= high) {
    			int mid = (low + high) >> 1;
    			if (get_lcp(p, mid) >= 2 * len + 1) low = (R = mid) + 1;
    			else high = mid - 1;
    		}

    		maximize(ans, 1ll * real_len * (R - L + 1));
    	};

    	if (i - start_len >= 0 && i + start_len < n && isPalin(i - start_len, i + start_len)) work(start_len);

    	for (int len = start_len + 1; ; ++len) {
    		if (i - len < 0 || i + len >= n) break;
    		if (t[i - len] != t[i + len]) break;
    		work(len);
    	}
    }

    cout << ans;
    return 0;
}

• Subtask 1: 0 / 8
• Subtask 2: 0 / 15
• Subtask 3: 0 / 24
• Subtask 4: 0 / 26
• Subtask 5: 0 / 27