Submission #204748

#	Time	Username	Problem	Language	Result	Execution time	Memory
204748		staniewzki	Palindromes (APIO14_palindrome)	C++17	100 / 100	606 ms	31428 KiB

palindrome

#include<bits/stdc++.h>
using namespace std;
 
ostream& operator<<(ostream &out, string str) {
	for(char c : str) out << c;
	return out;
}
 
template<class L, class R> ostream& operator<<(ostream &out, pair<L, R> p) {
	return out << "(" << p.first << ", " << p.second << ")";
}
 
template<class T> auto operator<<(ostream &out, T a) -> decltype(a.begin(), out) {
	out << "{";
	for(auto it = a.begin(); it != a.end(); it = next(it))
		out << (it != a.begin() ? ", " : "") << *it;
	return out << "}";
}
 
void dump() { cerr << "\n"; }
template<class T, class... Ts> void dump(T a, Ts... x) {
	cerr << a << ", ";
	dump(x...);
}
 
#ifdef DEBUG
#  define debug(...) cerr << "[" #__VA_ARGS__ "]: ", dump(__VA_ARGS__)
#else
#  define debug(...) false
#endif
 
#define REP(i, n) for(int i = 0; i < n; i++)
#define FOR(i, a, b) for(int i = a; i <= b; i++)
#define ST first
#define ND second
 
template<class T> int size(T && a) { return a.size(); }
 
using LL = long long;
using PII = pair<int, int>;

struct SuffixArray {
	vector<int> sa, lcp, rank;
	SuffixArray(string& s, int lim = 256) { // lub basic_string<int>
		int n = size(s) + 1, k = 0, a, b;
		vector<int> x(s.begin(), s.end() + 1);
		vector<int> y(n), ws(max(n, lim));
		sa = lcp = rank = y;
		iota(sa.begin(), sa.end(), 0);

		for(int j = 0, p = 0; p < n; j = max(1, j * 2), lim = p) {
			p = j;
			iota(y.begin(), y.end(), n - j);
			REP(i, n) if(sa[i] >= j)
				y[p++] = sa[i] - j;
			fill(ws.begin(), ws.end(), 0);
			REP(i, n) ws[x[i]]++;
			FOR(i, 1, lim - 1) ws[i] += ws[i - 1];
			for(int i = n; i--;) sa[--ws[x[y[i]]]] = y[i];
			swap(x, y);
			p = 1, x[sa[0]] = 0;
			FOR(i, 1, n - 1) a = sa[i - 1], b = sa[i], x[b] =
				(y[a] == y[b] && y[a + j] == y[b + j]) ? p - 1 : p++;
		}
		FOR(i, 1, n - 1) rank[sa[i]] = i;
		for(int i = 0, j; i < n - 1; lcp[rank[i++]] = k)
			for(k && k--, j = sa[rank[i] - 1];
				s[i + k] == s[j + k]; k++);
	}
	int operator[](int x) { return sa[x]; }
};

struct RMQ {
	vector<vector<int>> st;
	vector<int> pre;
	RMQ(vector<int> a) {
		int n = size(a), lg = 0;
		while((1 << lg) < n) lg++;
		st.resize(lg + 1, vector<int>(a));
		st[0] = a;
		FOR(i, 1, lg) REP(j, n) {
			st[i][j] = st[i - 1][j];
			int q = j + (1 << (i - 1));
			if(q < n) st[i][j] = min(st[i][j], st[i - 1][q]);
		}
		pre.resize(n + 1);
		FOR(i, 2, n) pre[i] = pre[i / 2] + 1;
	}

	int query(int l, int r) {
		int q = pre[r - l + 1], x = r - (1 << q) + 1;
		return min(st[q][l], st[q][x]);
	}
};

array<vector<int>, 2> manacher(string &in) {
	int n = size(in);
	array<vector<int>, 2> radius = {{vector<int>(n - 1), vector<int>(n)}};
	REP(parity, 2) {
		int z = parity ^ 1, L = 0, R = 0;
		REP(i, n - z) {
			int &rad = radius[parity][i];
			if(i <= R - z)
				rad = min(R - i, radius[parity][L + (R - i - z)]);
			int l = i - rad + z, r = i + rad;
			while(0 <= l - 1 && r + 1 < n && in[l - 1] == in[r + 1])
				++rad, ++r, --l;
			if(r > R)
				L = l, R = r;
		}
	}
	return radius;
}

int main() {
	ios_base::sync_with_stdio(0);
	cin.tie(0);

	string str;
	cin >> str;

	int n = size(str);
	SuffixArray sa(str);
	RMQ rmq(sa.lcp);

	auto get_lcp = [&](int i, int j) {
		if(i == j) return n - i;
		i = sa.rank[i], j = sa.rank[j];
		if(i > j) swap(i, j);
		return rmq.query(i + 1, j);
	};

	auto compare = [&](int a, int b, int i, bool equal) {
		int l = get_lcp(a, i);
		if(l >= b - a + 1) return equal;
		if(i + l == n) return false;
		return str[a + l] < str[i + l];
	};

	auto binsearch = [&](int a, int b, bool equal) {
		int l = 1, r = n + 1;
		while(l < r) {
			int mid = (l + r) / 2;
			if(compare(a, b, sa[mid], equal))
				r = mid;
			else
				l = mid + 1;
		}
		return l;
	};

	auto count = [&](int a, int b) -> LL {
		return binsearch(a, b, false) - binsearch(a, b, true);
	};

	auto m = manacher(str);
	LL ans = 0;
	REP(p, 2) REP(i, n + p - 1) {
		int l = i - m[p][i] + 1 - p;
		int r = i + m[p][i];
		if(l <= r) ans = max(ans, count(l, r) * (r - l + 1));
	}

	cout << ans << "\n";
}

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