Submission #64286

#	Time	Username	Problem	Language	Result	Execution time	Memory
64286		qkxwsm	Palindromes (APIO14_palindrome)	C++17	100 / 100	41 ms	20024 KiB

palindrome

/*
PROG: source
LANG: C++11
    _____
  .'     '.
 /  0   0  \
|     ^     |
|  \     /  |
 \  '---'  /
  '._____.'
*/
#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>

using namespace std;
using namespace __gnu_pbds;

struct chash
{
        int operator()(int x) const
        {
                x ^= (x >> 20) ^ (x >> 12);
                return x ^ (x >> 7) ^ (x >> 4);
        }
        int operator()(long long x) const
        {
                return x ^ (x >> 32);
        }
};

template<typename T> using orderedset = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename T, typename U> using hashtable = gp_hash_table<T, U, chash>;

template<class T>
void readi(T &x)
{
	T input = 0;
	bool negative = false;
	char c = ' ';
	while (c < '-')
        {
		c = getchar();
	}
	if (c == '-')
	{
		negative = true;
		c = getchar();
	}
	while (c >= '0')
	{
		input = input * 10 + (c - '0');
		c = getchar();
	}
	if (negative)
	{
		input = -input;
	}
	x = input;
}
template<class T>
void printi(T output)
{
	if (output == 0)
	{
		putchar('0');
		return;
	}
	if (output < 0)
	{
		putchar('-');
		output = -output;
	}
	int aout[20];
	int ilen = 0;
	while(output)
	{
		aout[ilen] = ((output % 10));
		output /= 10;
		ilen++;
	}
	for (int i = ilen - 1; i >= 0; i--)
	{
		putchar(aout[i] + '0');
	}
	return;
}
template<class T>
void ckmin(T &a, T b)
{
	a = min(a, b);
}
template<class T>
void ckmax(T &a, T b)
{
	a = max(a, b);
}
template<class T, class U>
T normalize(T x, U mod = 1000000007)
{
	return (((x % mod) + mod) % mod);
}
long long randomizell(long long mod)
{
	return ((1ll << 45) * rand() + (1ll << 30) * rand() + (1ll << 15) * rand() + rand()) % mod;
}
int randomize(int mod)
{
	return ((1ll << 15) * rand() + rand()) % mod;
}

#define y0 ___y0
#define y1 ___y1
#define MP make_pair
#define MT make_tuple
#define PB push_back
#define PF push_front
#define LB lower_bound
#define UB upper_bound
#define fi first
#define se second
#define debug(x) cerr << #x << " = " << x << endl;

const long double PI = 4.0 * atan(1.0);
const long double EPS = 1e-10;

#define MAGIC 347
#define SINF 10007
#define CO 1000007
#define INF 1000000007
#define BIG 1000000931
#define LARGE 1696969696967ll
#define GIANT 2564008813937411ll
#define LLINF 2696969696969696969ll
#define MAXN 300013

typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ld, ld> pdd;

int N, K;
int s[MAXN];
int child[30][MAXN];
int link[MAXN];
int len[MAXN];
int freq[MAXN];
ll ans;

void ins()
{
        //0 has length -1, 1 has length 0
        link[0] = 0; link[1] = 0;
        len[0] = -1; len[1] = 0;
        K = 2;
        int node = 0;
        for (int i = 0; i < N; i++)
        {
                // cerr << "insert pos " << i << endl;
                int c = s[i];
                while(node && s[i - 1 - len[node]] != c)
                {
                        // cerr << i << " check " << node << endl;
                        node = link[node];
                }
                // cerr << "node = " << node << endl;
                if (child[c][node])
                {
                        node = child[c][node];
                }
                else
                {
                        len[K] = len[node] + 2;
                        child[c][node] = K;
                        //FIND THE LINK FOR THIS NODE!
                        node = link[node];
                        // cerr << "node = " << node << endl;
                        if (len[K] == 1)
                        {
                                link[K] = 1;
                        }
                        else
                        {
                                while(node && s[i - 1 - len[node]] != c)
                                {
                                        node = link[node];
                                }
                                link[K] = child[c][node];
                        }
                        // cerr << "link " << K << " = " << link[K] << endl;
                        node = K;
                        K++;
                }
                freq[node]++;
                // cerr << node << ' ' << freq[node] << endl;
                // cerr << "length " << node << " = " << len[node] << "; value = ";
                // for (int j = i - len[node] + 1; j <= i; j++)
                // {
                //         cerr << (char) ('a' - 1 + s[j]);
                // }
                // cerr << endl;
        }
        return;
}

int32_t main()
{
	ios_base::sync_with_stdio(0);
	srand(time(0));
	//	cout << fixed << setprecision(10);
	//	cerr << fixed << setprecision(10);
	if (fopen("input.in", "r"))
	{
		freopen ("input.in", "r", stdin);
		freopen ("output.out", "w", stdout);
	}
        string temps;
        cin >> temps;
        N = temps.length();
        for (int i = 0; i < N; i++)
        {
                s[i] = temps[i] - 'a' + 1;
        }
        ins();
        // for (int i = 2; i <= K; i++)
        // {
        //         cerr << freq[i] << ' ';
        // }
        // cerr << endl;
        for (int i = K - 1; i >= 2; i--)
        {
                // cerr << "freq " << link[i] << " += " << "freq " << i << endl;
                freq[link[i]] += freq[i];
        }
        // for (int i = 2; i <= K; i++)
        // {
        //         cerr << freq[i] << ' ';
        // }
        // cerr << endl;
        for (int i = 2; i < K; i++)
        {
                ckmax(ans, 1ll * freq[i] * len[i]);
        }
        cout << ans << '\n';
	//	cerr << "time elapsed = " << (clock() / (CLOCKS_PER_SEC / 1000)) << " ms" << endl;
	return 0;
}

Compilation message (stderr)

palindrome.cpp: In function 'int32_t main()':
palindrome.cpp:215:11: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
   freopen ("input.in", "r", stdin);
   ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
palindrome.cpp:216:11: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
   freopen ("output.out", "w", stdout);
   ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~

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