Submission #917066

#	Time	Username	Problem	Language	Result	Execution time	Memory
917066		sleepntsheep	Three Friends (BOI14_friends)	C++17	100 / 100	61 ms	35660 KiB

friends

#include <iostream>
#include <fstream>
#include <iomanip>
#include <cmath>
#include <cassert>
#include <cstring>
#include <math.h>
#include <vector>
#include <algorithm>
#include <deque>
#include <set>
#include <utility>
#include <array>
#include <complex>

using u32 = unsigned;
using i32 = int;
using i64 = long long;
using u64 = unsigned long long;
using f64 = double;
using f80 = long double;

using namespace std;
using pt = complex<f80>;
#define ALL(x) begin(x), end(x)
#define ShinLena cin.tie(nullptr)->sync_with_stdio(false);
#define N 2000005

string u;
int n;


i64 bpowc(i64 a, i64 b, i64 m)
{
    if (!b) return 1;
    i64 r = bpowc(a, b>>1, m);
    if (b&1) return r*r%m*a%m;
    return r*r%m;
}

/*
constexpr array<i64, 2> Hash[] = {{137, 1000000007}, {61, 1000000009}, {31, 969414643},
    {281, 969414643}
};
*/

constexpr array<i64, 2> Hash[] = {{137, 1000000007}
};


constexpr int HH = sizeof Hash / sizeof Hash[0];

i64 a[HH][N], bp[HH][N], ib[HH];


int main()
{
    ShinLena;
    cin >> n >> u;
    u = " " + u;

    for (int h = 0; h < HH; ++h)
    {
        bp[h][0] = 1;
        for (int i = 1; i <= n + 1; ++i) bp[h][i] = bp[h][i-1] * Hash[h][0] % Hash[h][1];
        ib[h] = bpowc(Hash[h][0], Hash[h][1] - 2, Hash[h][1]);

        for (int i = 1; i <= n; ++i)
            a[h][i] = (a[h][i-1] + (u[i] - 'A' + 2) * bp[h][i-1] % Hash[h][1]) % Hash[h][1];
    }


    set<array<i64, HH>> S;
    int at = 0;
    for (int i = 1; i <= n; ++i)
    {
        int eq = 0;
        array<i64, HH> ah{};
        if (i > n / 2)
        {
            for (int h = 0; h < HH; ++h)
            {
                i64 fst = a[h][n/2];
                i64 lst = (a[h][i-1] - a[h][n/2] + Hash[h][1]) % Hash[h][1];
                lst = (lst + (a[h][n] - a[h][i] + Hash[h][1]) % Hash[h][1] * ib[h] % Hash[h][1]) % Hash[h][1];
                ah[h] = fst;
                fst = fst * bp[h][n/2] % Hash[h][1];
                if (fst == lst) ++eq;
            }
            if (eq == HH) S.insert(ah), at = i;
        }
        else
        {
            for (int h = 0; h < HH; ++h)
            {
                i64 fst = (a[h][i-1] + (a[h][n/2+1] - a[h][i] + Hash[h][1]) % Hash[h][1]
                        * ib[h] % Hash[h][1]) % Hash[h][1];
                i64 lst = (a[h][n] - a[h][n/2+1] + Hash[h][1]) % Hash[h][1];
                ah[h] = fst;
                fst = fst * bp[h][n/2+1] % Hash[h][1];

                if (fst == lst) ++eq;
            }
            if (eq == HH) S.insert(ah), at = i;
        }
    }

    if (S.empty())
    {
        cout << "NOT POSSIBLE";
    }
    else if (S.size() > 1)
    {
        cout << "NOT UNIQUE";
    }
    else
    {
        u.erase(u.begin() + at);
        cout << u.substr(1, n/2);
    }

    return 0;
}

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