Submission #879410

#	Time	Username	Problem	Language	Result	Execution time	Memory
879410		marvinthang	Palindromes (APIO14_palindrome)	C++17	100 / 100	292 ms	71520 KiB

palindrome

/*************************************
*    author: marvinthang             *
*    created: 27.11.2023 15:58:18    *
*************************************/

#include <bits/stdc++.h>

using namespace std;

#define                  fi  first
#define                  se  second
#define                left  ___left
#define               right  ___right
#define                TIME  (1.0 * clock() / CLOCKS_PER_SEC)
#define             MASK(i)  (1LL << (i))
#define           BIT(x, i)  ((x) >> (i) & 1)
#define  __builtin_popcount  __builtin_popcountll
#define              ALL(v)  (v).begin(), (v).end()
#define           REP(i, n)  for (int i = 0, _n = (n); i < _n; ++i)
#define          REPD(i, n)  for (int i = (n); i-- > 0; )
#define        FOR(i, a, b)  for (int i = (a), _b = (b); i < _b; ++i) 
#define       FORD(i, b, a)  for (int i = (b), _a = (a); --i >= _a; ) 
#define       FORE(i, a, b)  for (int i = (a), _b = (b); i <= _b; ++i) 
#define      FORDE(i, b, a)  for (int i = (b), _a = (a); i >= _a; --i) 
#define        scan_op(...)  istream & operator >> (istream &in, __VA_ARGS__ &u)
#define       print_op(...)  ostream & operator << (ostream &out, const __VA_ARGS__ &u)
#ifdef LOCAL
    #include "debug.h"
#else
    #define file(name) if (fopen(name".inp", "r")) { freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout); }
    #define DB(...) 23
    #define db(...) 23
    #define debug(...) 23
#endif

template <class U, class V> scan_op(pair <U, V>)  { return in >> u.first >> u.second; }
template <class T> scan_op(vector <T>)  { for (size_t i = 0; i < u.size(); ++i) in >> u[i]; return in; }
template <class U, class V> print_op(pair <U, V>)  { return out << '(' << u.first << ", " << u.second << ')'; }
template <size_t i, class T> ostream & print_tuple_utils(ostream &out, const T &tup) { if constexpr(i == tuple_size<T>::value) return out << ")";  else return print_tuple_utils<i + 1, T>(out << (i ? ", " : "(") << get<i>(tup), tup); }
template <class ...U> print_op(tuple<U...>) { return print_tuple_utils<0, tuple<U...>>(out, u); }
template <class Con, class = decltype(begin(declval<Con>()))> typename enable_if <!is_same<Con, string>::value, ostream&>::type operator << (ostream &out, const Con &con) { out << '{'; for (__typeof(con.begin()) it = con.begin(); it != con.end(); ++it) out << (it == con.begin() ? "" : ", ") << *it; return out << '}'; }
template <class A, class B> bool minimize(A &a, B b)  { if (a > b) { a = b; return true; } return false; }
template <class A, class B> bool maximize(A &a, B b)  { if (a < b) { a = b; return true; } return false; }

// end of template

const int BASE = 31;

void process(void) {
	string s; cin >> s;

	auto manacher_odd = [&] (string s) {
		int n = s.size();
		s = '$' + s + '^';
		vector <int> p(n + 1);
		int l = 1, r = 1;
		FORE(i, 1, n) {
			p[i] = max(0, min(r - i, p[l + r - i]));
			while (s[i - p[i]] == s[i + p[i]]) ++p[i];
			if (i + p[i] > r) r = i + p[i], l = i - p[i];
		}
		return vector(1 + ALL(p));
	};
	auto manacher = [&] (string s) {
		string t;
		for (char c: s) t += string("#") + c;
		auto res = manacher_odd(t + "#");
		for (int &x: res) x >>= 1;
		return vector(1 + ALL(res) - 1);
	};
	auto pl = manacher(s);
	s = s + '#';
	int n = s.size();
	vector <int> pos(n), cnt(n), lcp(n);
	iota(ALL(pos), 0);
	sort(ALL(pos), [&] (int a, int b) { return s[a] < s[b]; });
	cnt[pos[0]] = 0;
	FOR(i, 1, n) cnt[pos[i]] = cnt[pos[i - 1]] + (s[pos[i]] != s[pos[i - 1]]);
	auto countSort = [&] (vector <int> &p, vector <int> &c) {
		vector <int> pos(n), new_p(n);
		for (int &x: c) if (x + 1 < n) ++pos[x + 1];
		partial_sum(ALL(pos), pos.begin());
		for (int &x: p) new_p[pos[c[x]]++] = x;
		p = move(new_p);
	};
	for (int k = 1; k < n; k <<= 1) {
		REP(i, n) {
			pos[i] = pos[i] - k;
			if (pos[i] < 0) pos[i] += n;
		}
		countSort(pos, cnt);
		vector <int> new_c(n);
		new_c[pos[0]] = 0;
		pair <int, int> prv(cnt[pos[0]], cnt[pos[0] + k - (pos[0] + k < n ? 0 : n)]);
		FOR(i, 1, n) {
			pair <int, int> cur(cnt[pos[i]], cnt[pos[i] + k - (pos[i] + k < n ? 0 : n)]);
			new_c[pos[i]] = new_c[pos[i - 1]] + (prv != cur);
			prv = cur;
		}
		cnt = move(new_c);
	}
	for (int i = 0, k = 0; i < n - 1; ++i) {
		int j = pos[cnt[i] - 1];
		while (s[i + k] == s[j + k]) ++k;
		lcp[cnt[i]] = k;
		k = max(k - 1, 0);
	}
	vector <vector <int>> add_odd(n), add_even(n), del_odd(n), del_even(n);
	REP(i, pl.size()) if (pl[i]) {
		int p = i / 2;
		if (i & 1) {
			add_even[p - pl[i] + 1].push_back(p);
			del_even[p + pl[i]].push_back(p);
		} else {
			add_odd[p - pl[i] + 1].push_back(p);
			del_odd[p + pl[i] - 1].push_back(p);
		}
	}
	set <int> ms_odd, ms_even;
	vector <int> max_palin(n, 0);
	REP(i, n - 1) {
		for (int x: add_odd[i]) ms_odd.insert(x);
		for (int x: add_even[i]) ms_even.insert(x);
		int upper = lcp[cnt[i]];
		if (upper + 2 * i - 1 >= 0) {
			auto it = ms_odd.upper_bound((upper + 2 * i - 1) / 2);
			if (it != ms_odd.begin()) maximize(max_palin[i], (*prev(it) - i) * 2 + 1);
		}
		if (upper + 2 * i - 2 >= 0) {
			auto it = ms_even.upper_bound((upper + 2 * i - 2) / 2);
			if (it != ms_even.begin()) maximize(max_palin[i], (*prev(it) - i + 1) * 2);
		}
		for (int x: del_odd[i]) ms_odd.erase(x);
		for (int x: del_even[i]) ms_even.erase(x);
	}
	stack <int> st;
	vector <int> left(n);
	REP(i, n) {
		while (!st.empty() && lcp[st.top()] >= lcp[i]) st.pop();
		left[i] = st.empty() ? 0 : st.top();
		st.push(i);
	}
	while (!st.empty()) st.pop();
	long long res = 0;
	REP(i, pl.size()) maximize(res, pl[i] * 2 - !(i & 1));
	REPD(i, n) {
		while (!st.empty() && lcp[st.top()] >= lcp[i]) st.pop();
		maximize(res, 1LL * ((st.empty() ? n : st.top()) - left[i]) * max_palin[pos[i]]);
		st.push(i);
	}
	cout << res << '\n';
}

int main(void) {
	ios_base::sync_with_stdio(false); cin.tie(nullptr); // cout.tie(nullptr);
	file("palindrome");
	// int t; cin >> t; while (t--)
	process();
	// cerr << "Time elapsed: " << TIME << " s.\n";
	return (0^0);
}

Compilation message (stderr)

palindrome.cpp: In function 'int main()':
palindrome.cpp:30:61: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   30 |     #define file(name) if (fopen(name".inp", "r")) { freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout); }
      |                                                      ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
palindrome.cpp:156:2: note: in expansion of macro 'file'
  156 |  file("palindrome");
      |  ^~~~
palindrome.cpp:30:94: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   30 |     #define file(name) if (fopen(name".inp", "r")) { freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout); }
      |                                                                                       ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
palindrome.cpp:156:2: note: in expansion of macro 'file'
  156 |  file("palindrome");
      |  ^~~~

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