Submission #1124077

#	Time	Username	Problem	Language	Result	Execution time	Memory
1124077		JanPham	Three Friends (BOI14_friends)	C++20	0 / 100	1101 ms	96440 KiB

friends

#include <bits/stdc++.h>
 
using namespace std;
 
#define pb push_back
#define fi first
#define se second
#define TranLeThanhTam "TranLeThanhTam"
#define all(v) v.begin(),v.end()
#define reset(a,i) memset(a,i,sizeof(a))
#define FOR(i,a,b) for (int i = (a), _b = (b); i <= _b; ++i)
#define FORD(i,a,b) for (int i = (a), _b = (b); i >= _b; --i)
#define compact(v) sort(all(v)), v.erase(unique(all(v)), end(v))
#define sz(v) (int) v.size()
#define MASK(i) (1 << (i))
 
typedef long long ll;
typedef long double lb;
typedef pair<ll,ll> pll;
typedef pair<int,int> pii;
 
const int Thanh_Tam = 2 * 1e6 + 17;
const int inf = 1e9 + 17;
const long long infll = 1e18 + 17;
const int MOD = 1e9 + 7;
const int Log = 18;
const int dx[4] = {-1, 0, 0, 1};
const int dy[4] = {0, -1, 1, 0};
const int max_block_size = 270;
const ll P = 757;
const int maxA = 1e2 + 17;
const int addi = 1e9;
const char dir[4] = {'W', 'S', 'N', 'E'};
const int Mod[3] = {998244353, MOD, 759186269};
 
ll mul(ll a, ll b, ll mod);
ll binpow(ll a, ll b, ll mod)
{
    ll res = 1;
    while (b > 0)
    {
        if (b & 1) res = mul(res,a,mod);
        b >>= 1;
        a = mul(a,a,mod);
    }
    return res;
}
ll add(ll a, ll b, ll mod) { return (a + b) % mod;                 }
ll sub(ll a, ll b, ll mod) { return (a - b + mod) % mod;          }
ll mul(ll a, ll b, ll mod) { return ((a % mod) * (b % mod)) % mod; }
ll div(ll a, ll b, ll mod) { return mul(a, binpow(b, mod - 2, mod), mod); }
 
mt19937 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
ll rand_range(ll l, ll r) { return uniform_int_distribution<ll>(l,r)(rng); }

int n, ans = 0;
string s, res; 
ll Pow[Thanh_Tam][3], pref[Thanh_Tam][3];

ll get(int l, int r, int type)
{
    return div(sub(pref[r][type], pref[l - 1][type], Mod[type]), Pow[l - 1][type], Mod[type]);
}

void ThanhTam()
{
    cin >> n >> s;
    s = ' ' + s;

    if ((n + 1) & 1)
    {
        cout << "NOT POSSIBLE";
        return;
    }

    FOR(j,0,2) Pow[0][j] = 1;

    FOR(i,1,n)
        FOR(j,0,2)
        {
            Pow[i][j] = mul(Pow[i - 1][j], P, Mod[j]);
            pref[i][j] = add(pref[i - 1][j], mul(s[i] - 'A', Pow[i][j], Mod[j]), Mod[j]);
        }

    int Mid = (n + 1) >> 1;
    FOR(i,1,Mid)
    {
        bool possible = true;
        FOR(j,0,2)
        {
            ll value_left = add(get(1, i - 1, j), mul(get(i + 1, Mid, j), Pow[i - 1][j], Mod[j]), Mod[j]), value_right = get(Mid + 1, n, j);
            if (value_left != value_right) possible = false;
        }

        ans += possible; 
        if (ans > 1)
        {
            cout << "NOT UNIQUE";
            return;
        }
        if (possible) res = s.substr(Mid + 1, n - Mid);
    }
    
    FOR(i,Mid + 1, n)
    {
        bool possible = true;
        FOR(j,0,2)
        {
            ll value_left = get(1, Mid - 1, j), value_right = add(get(Mid, i - 1, j), mul(get(i + 1, n, j), Pow[i - Mid][j], Mod[j]), Mod[j]);
            if (value_left != value_right) possible = false;
        }

        ans += possible; 
        if (ans > 1)
        {
            cout << "NOT UNIQUE";
            return;
        }
        if (possible) res = s.substr(1, Mid - 1);
    }

    if (ans == 0)
    {
        cout << "NOT POSSIBLE";
        return;
    }
    cout << res;

    return;
}
 
signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
 
    if (fopen(TranLeThanhTam".inp","r"))
    {
        freopen(TranLeThanhTam".inp","r",stdin);
        freopen(TranLeThanhTam".out","w",stdout);
    }
 
    int t = 1;
    //cin >> t;
    while (t--)
        ThanhTam();
 
    return 0;
}

Compilation message (stderr)

friends.cpp: In function 'int main()':
friends.cpp:140:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  140 |         freopen(TranLeThanhTam".inp","r",stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
friends.cpp:141:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  141 |         freopen(TranLeThanhTam".out","w",stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 35
• Subtask 2: 0 / 65