Submission #48020

#	Time	Username	Problem	Language	Result	Execution time	Memory
48020		E869120	Palindromes (APIO14_palindrome)	C++14	47 / 100	1082 ms	19204 KiB

palindrome

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <map>
using namespace std;

string S; int L[100009], N, col[100009], cnts; vector<int>x[100009], y[100009];

long long Get(int pos) {
	if (pos < 0) return -1;
	if (pos >= N) return -2;
	return L[pos];
}

long long roll1[1009][1009], roll2[1009][1009];

void solve_naive() {
	map<long long, long long>M;

	for (int i = 0; i < S.size(); i++) {
		for (int j = i; j < S.size(); j++) {
			if (j != 0) roll1[i][j] = roll1[i][j - 1] * 331LL;
			roll1[i][j] += (S[j] - 'a' + 1);
		}
	}
	for (int i = 0; i < S.size(); i++) {
		for (int j = i; j >= 0; j--) {
			roll2[i][j] = roll2[i][j + 1] * 331LL;
			roll2[i][j] += (S[j] - 'a' + 1);
		}
	}
	long long maxn = 0;
	for (int i = 0; i < S.size(); i++) {
		for (int j = i; j < S.size(); j++) {
			if (roll1[i][j] != roll2[j][i]) continue;
			M[roll1[i][j]] += (j - i + 1);
			maxn = max(maxn, M[roll1[i][j]]);
		}
	}
	cout << maxn << endl;
}

int main() {
	cin >> S; N = S.size();
	if (S.size() == 1) { cout << "1" << endl; return 0; }
	if (S.size() <= 1000) { solve_naive(); return 0; }
	for (int i = 0; i < N; i++) L[i] = (S[i] - 'a');
	for (int i = 0; i < N; i++) x[0].push_back(i);

	long long maxn = 0; cnts = 1;

	for (int i = 0; i <= N / 2 + 1; i++) {
		int cnt = 0;
		for (int j = 0; j < cnts; j++) {
			if (x[j].size() == 1) { int to = x[j][0]; if (Get(to - i) == Get(to + i)) { y[cnt] = x[j]; cnt++; } continue; }

			vector<int>H[26];
			for (int k = 0; k < x[j].size(); k++) {
				int to = x[j][k];
				if (Get(to - i) != Get(to + i)) continue;
				H[Get(to + i)].emplace_back(to);
			}
			for (int k = 0; k < 26; k++) {
				if (H[k].size() >= 1) { y[cnt] = H[k]; cnt++; }
			}
		}
		for (int j = 0; j < cnt; j++) { x[j] = y[j]; maxn = max(maxn, 1LL * (long long)x[j].size()*(i * 2 + 1)); } cnts = cnt;
	}

	for (int i = 0; i < 100009; i++) x[i].clear(); cnts = 1;
	for (int i = 0; i < N; i++) x[0].push_back(i);

	for (int i = 0; i <= N / 2 + 1; i++) {
		int cnt = 0;
		for (int j = 0; j < cnts; j++) {
			if (x[j].size() == 1) { int to = x[j][0]; if (Get(to - i) == Get(to + i)) { y[cnt] = x[j]; cnt++; } continue; }

			vector<int>H[26];
			for (int k = 0; k < x[j].size(); k++) {
				int to = x[j][k];
				if (Get(to - i) != Get(to + i + 1)) continue;
				H[Get(to + i)].emplace_back(to);
			}
			for (int k = 0; k < 26; k++) {
				if (H[k].size() >= 1) { y[cnt] = H[k]; cnt++; }
			}
		}
		for (int j = 0; j < cnt; j++) { x[j] = y[j]; maxn = max(maxn, 1LL * (long long)x[j].size()*(i * 2 + 2)); }
		cnts = cnt;
	}
	cout << maxn << endl;
	return 0;
}

Compilation message (stderr)

palindrome.cpp: In function 'void solve_naive()':
palindrome.cpp:21:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < S.size(); i++) {
                  ~~^~~~~~~~~~
palindrome.cpp:22:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int j = i; j < S.size(); j++) {
                   ~~^~~~~~~~~~
palindrome.cpp:27:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < S.size(); i++) {
                  ~~^~~~~~~~~~
palindrome.cpp:34:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < S.size(); i++) {
                  ~~^~~~~~~~~~
palindrome.cpp:35:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int j = i; j < S.size(); j++) {
                   ~~^~~~~~~~~~
palindrome.cpp: In function 'int main()':
palindrome.cpp:59:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (int k = 0; k < x[j].size(); k++) {
                    ~~^~~~~~~~~~~~~
palindrome.cpp:71:2: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
  for (int i = 0; i < 100009; i++) x[i].clear(); cnts = 1;
  ^~~
palindrome.cpp:71:49: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
  for (int i = 0; i < 100009; i++) x[i].clear(); cnts = 1;
                                                 ^~~~
palindrome.cpp:80:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (int k = 0; k < x[j].size(); k++) {
                    ~~^~~~~~~~~~~~~

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