Submission #63131

#	Time	Username	Problem	Language	Result	Execution time	Memory
63131		qkxwsm	Three Friends (BOI14_friends)	C++17	35 / 100	1087 ms	145052 KiB

friends

/*
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 SLLINF 10007
#define CO 1000007
#define INF 1000000007
#define BIG 1000000931
#define LARGE 1696969696967ll
#define GIANT 2564008813937411ll
#define LLINF 2696969696969696969ll
#define MAXN 2000013

typedef __int128_t ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ld, ld> pdd;

int N;
int arr[MAXN];
ll pw[MAXN];
ll pref[MAXN];
hashtable<long long, int> hashes;
int res = -1;

ll getpw(ll a, ll e, ll mod)
{
        if (e == 1)
        {
                return a;
        }
        ll was = getpw(a, e / 2, mod);
        if (e % 2)
        {
                return was * was % mod * a % mod;
        }
        else
        {
                return was * was % mod;
        }
}
ll modinv(ll a, ll mod)
{
        return getpw(a, mod - 2, mod);
}
ll gethash(int l, int r)
{
        ll res = {pref[r + 1] - pref[l] * pw[r - l + 1]};
        res = normalize(res, LLINF);
        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);
	}
        // N = 1999999;
        readi(N);
        if (N % 2 == 0)
        {
                puts("NOT POSSIBLE\n");
                return 0;
        }
        for (int i = 0; i < N; i++)
        {
                char c = getchar();
                // char c = 'A';
                arr[i] = c - 'A' + 1;
        }
        pw[0] = 1;
        for (int i = 1; i <= N; i++)
        {
                pw[i] = pw[i - 1] * CO;
                pw[i] %= LLINF;
        }
        pref[0] = 0;
        for (int i = 0; i < N; i++)
        {
                pref[i + 1] = pref[i] * CO + arr[i];
                pref[i + 1] %= LLINF;
        }
        for (int i = 0; i <= (N + 1) / 2; i++)
        {
                ll go = gethash(i, i + (N / 2) - 1);
                go *= (pw[N / 2] + 1); go %= LLINF;
                hashes[go] = i;
        }
        for (int i = 0; i < N; i++)
        {
                //remove i
                ll cur = (gethash(0, i - 1) * pw[N - i - 1] + gethash(i + 1, N - 1)) % LLINF;
                if (hashes.find(cur) == hashes.end())
                {
                        continue;
                }
                int pos = hashes[cur];
                if (res != -1 && pos != res && pos != 0)
                {
                        puts("NOT UNIQUE");
                        return 0;
                }
                res = pos;
        }
        if (res == -1)
        {
                puts("NOT POSSIBLE");
                return 0;
        }
        for (int i = res; i < res + (N / 2); i++)
        {
                putchar((char) (arr[i] + 'A' - 1));
        }
        putchar('\n');
	// cerr << "time elapsed = " << (clock() / (CLOCKS_PER_SEC / 1000)) << " ms" << endl;
	return 0;
}

Compilation message (stderr)

friends.cpp: In function 'int32_t main()':
friends.cpp:185:11: 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);
   ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
friends.cpp:186:11: 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: 35 / 35
• Subtask 2: 0 / 65