Submission #63859

#	Time	Username	Problem	Language	Result	Execution time	Memory
63859		qkxwsm	Palindromes (APIO14_palindrome)	C++17	23 / 100	1077 ms	109556 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;
int s[MAXN], t[2 * MAXN];
int len[2 * MAXN];
vector<int> sse[MAXN], sfi[MAXN];
int suf[MAXN], srank[MAXN], lcp[MAXN];
int sparse[25][MAXN];
int sval[25][MAXN];
ll ans = 0;

void manacher()
{
        int lt = 0, rt = 0;
        for (int i = 0; i <= 2 * N; i++)
        {
                len[i] = min(rt - i, len[lt + (rt - i)]);
                while(0 <= i - len[i] && i + len[i] <= 2 * N && t[i - len[i]] == t[i + len[i]])
                {
                        len[i]++;
                }
                if (i + len[i] > rt)
                {
                        lt = i - len[i];
                        rt = i + len[i];
                }
                len[i]--;
        }
        return;
}
void buildsuf()
{
        for (int i = 0; i < N; i++)
        {
                sval[0][i] = s[i];
        }
        for (int i = 0; i < 20; i++)
        {
                int Z = max(30, N);
                for (int j = 0; j <= Z; j++)
                {
                        sse[j].clear();
                        sfi[j].clear();
                }
                for (int j = 0; j < N; j++)
                {
                        int val1 = (((j + (1 << i)) >= N) ? 0 : sval[i][j + (1 << i)]);
                        sse[val1].PB(j);
                }
                for (int j = 0; j <= Z; j++)
                {
                        for (int idx : sse[j])
                        {
                                int val = sval[i][idx];
                                sfi[val].PB(idx);
                        }
                }
                pii was = {-1, -1}; int K = 0;
                for (int j = 0; j <= Z; j++)
                {
                        for (int idx : sfi[j])
                        {
                                pii cur = {sval[i][idx], ((idx + (1 << i)) >= N ? 0 : sval[i][idx + (1 << i)])};
                                if (cur > was)
                                {
                                        K++;
                                        was = cur;
                                }
                                sval[i + 1][idx] = K;
                        }
                }
        }
        for (int i = 0; i < N; i++)
        {
                srank[i] = sval[20][i] - 1;
                suf[srank[i]] = i;
        }
        int best = 0;
        for (int i = 0; i < N; i++)
        {
                int idx = srank[i];
                if (idx == N - 1)
                {
                        lcp[idx] = 0;
                        continue;
                }
                int j = suf[idx + 1];
                while(i + best < N && j + best < N && s[i + best] == s[j + best]) best++;
                lcp[idx] = best;
                if (best) best--;
        }
}
int query(int lt, int rt)
{
        int lg = 31 - __builtin_clz(rt - lt + 1);
        int res = min(sparse[lg][lt], sparse[lg][rt - (1 << lg) + 1]);
        return res;
        // cerr << "res = " << res << endl;
        // for (int j = lt; j <= rt; j++)
        // {
        //         cerr << lcp[j] << ' ';
        // }
        // cerr << endl;
}
int chk(int lt, int rt)
{
        int sz = rt - lt + 1, res = 1, cur = srank[lt], lo, hi;
        // cerr << "count " << lt << ' ' << rt << endl;
        lo = 0, hi = cur;
        while(hi > lo)
        {
                int mid = (hi + lo) / 2;
                if (query(mid, cur - 1) < sz)
                {
                        lo = mid + 1;
                }
                else
                {
                        hi = mid;
                }
        }
        res += (cur - lo);
        lo = cur - 1, hi = N - 2;
        while(hi > lo)
        {
                int mid = (hi + lo + 1) / 2;
                if (query(cur, mid) < sz)
                {
                        hi = mid - 1;
                }
                else
                {
                        lo = mid;
                }
        }
        res += (lo - cur + 1);
        // cerr << "res " << res << endl;
        return res;
}

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;
        }
        for (int i = 0; i < N; i++)
        {
                t[2 * i + 1] = s[i];
        }
        manacher();
        // for (int i = 0; i <= 2 * N; i++)
        // {
        //         cerr << t[i] << ' ';
        // }
        // cerr << endl;
        // for (int i = 0; i <= 2 * N; i++)
        // {
        //         cerr << len[i] << ' ';
        // }
        // cerr << endl;
        buildsuf();
        for (int i = 0; i < N - 1; i++)
        {
                sparse[0][i] = lcp[i];
        }
        for (int i = 1; i < 20; i++)
        {
                for (int j = 0; j < N - 1; j++)
                {
                        sparse[i][j] = min(sparse[i - 1][j], ((j + (1 << (i - 1)) < N - 1) ? sparse[i - 1][j + (1 << (i - 1))] : 0));
                }
        }
        // for (int i = 0; i < N; i++)
        // {
        //         cerr << suf[i] << endl;
        // }
        for (int i = 1; i < 2 * N; i++)
        {
                int lt, rt;
                if (i % 2)
                {
                        lt = (i / 2) - (len[i] / 2);
                        rt = (i / 2) + (len[i] / 2);
                }
                else
                {
                        lt = (i / 2) - (len[i] / 2);
                        rt = (i / 2) + (len[i] / 2) - 1;
                }
                if (lt > rt)
                {
                        continue;
                }
                while(lt <= rt)
                {
                        ckmax(ans, 1ll * (rt - lt + 1) * chk(lt, rt));
                        lt++; rt--;
                }
                // cerr << lt << ' ' << rt << endl;
        }
        // for (int i = 0; i <= 2 * N; i++)
        // {
        //         cerr << len[i] << ' ';
        // }
        // cerr << endl;
        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:289:11: 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:290:11: 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: 0 / 24
• Subtask 4: 0 / 26
• Subtask 5: 0 / 27