Submission #880887

#	Time	Username	Problem	Language	Result	Execution time	Memory
880887		vjudge1	Necklace (Subtask 1-3) (BOI19_necklace1)	C++17	25 / 85	1542 ms	5416 KiB

necklace

#include <bits/stdc++.h>
using namespace std;

#define ll long long 
#define pb push_back
#define pii array<int, 2>
#define piii array<int, 3>

#pragma GCC optimize("Ofast,unroll-loops")
#pragma GCC target("avx2")

int power(int a, ll b, int mod) {
    int ret = 1;
    for (; b; b >>= 1, a = 1ll * a * a % mod)
        if (b & 1)
            ret = 1ll * ret * a % mod;
    return ret;
}

const int N = 3e3 + 4;
const int P = 701, M[] = {(int) 1e9 + 7, (int) 1e9 + 9};
const int inv[] = {power(P, M[0] - 2, M[0]), power(P, M[1] - 2, M[1])};

int n[2], pw[N][2];
string s[2];

pii check(int sz) {
    vector<piii> hashes[2];
    for (int i = 0; i < 2; ++i) {
        for (int j = 0; j + sz - 1 < n[i]; ++j) {
            pii h = {0, 0};
            for (int k = j; k < j + sz; ++k) {
                for (int o = 0; o < 2; ++o) { 
                    h[o] = (h[o] + 1ll * s[i][k] * pw[k - j][o] % M[o]) % M[o];
                }
            }

            hashes[i].pb({h[0], h[1], j});
            for (int k = j + 1; k < j + sz; ++k) {
                for (int o = 0; o < 2; ++o) {
                    h[o] = (h[o] - s[i][k - 1] + M[o]) % M[o];
                    h[o] = 1ll * h[o] * inv[o] % M[o];
                    h[o] = (h[o] + 1ll * s[i][k - 1] * pw[sz - 1][o] % M[o]) % M[o];
                    hashes[i].pb({h[0], h[1], j});
                }
            }
        }
    }
    for (int i = 0; i < 2; ++i) {
        reverse(s[i].begin(), s[i].end());
    }

    for (int i = 0; i < 2; ++i) {
        for (int j = 0; j + sz - 1 < n[i]; ++j) {
            pii h = {0, 0};
            for (int k = j; k < j + sz; ++k) {
                for (int o = 0; o < 2; ++o) { 
                    h[o] = (h[o] + 1ll * s[i][k] * pw[k - j][o] % M[o]) % M[o];
                }
            }

            int t = j + sz - 1;
            hashes[i].pb({h[0], h[1], n[i] - t - 1});
            for (int k = j + 1; k < j + sz; ++k) {
                for (int o = 0; o < 2; ++o) {
                    h[o] = (h[o] - s[i][k - 1] + M[o]) % M[o];
                    h[o] = 1ll * h[o] * inv[o] % M[o];
                    h[o] = (h[o] + 1ll * s[i][k - 1] * pw[sz - 1][o] % M[o]) % M[o];
                    hashes[i].pb({h[0], h[1], n[i] - t - 1});
                }
            }
        }
    }
    for (int i = 0; i < 2; ++i) {
        reverse(s[i].begin(), s[i].end());
        sort(hashes[i].begin(), hashes[i].end());
    }

    int pt = 0;
    for (auto [h0, h1, idx] : hashes[0]) {
        while (h0 > hashes[1][pt][0]) {
            ++pt;
            if (pt == hashes[1].size()) {
                return {-1, -1};
            }
        }
        if (hashes[1][pt][0] == h0) {
            while (h0 == hashes[1][pt][0]) {
                if (h0 == hashes[1][pt][0] && h1 == hashes[1][pt][1]) {
                    return {idx, hashes[1][pt][2]};
                }
                ++pt;
                if (pt == hashes[1].size()) {
                    return {-1, -1};
                }
            }
        }
    }
    return {-1, -1};
}

signed main() {
    ios::sync_with_stdio(0);
    cin.tie(0);

    pw[0][0] = pw[0][1] = 1;
    for (int i = 1; i < N; ++i) {
        for (int j = 0; j < 2; ++j) {
            pw[i][j] = 1ll * pw[i - 1][j] * P % M[j];
        }
    }

    cin >> s[0] >> s[1];
    n[0] = s[0].size();
    n[1] = s[1].size();
    
    for (int i = min(n[0], n[1]); i > 0; --i) {
        pii res = check(i);
        if (res[0] != -1) {
            cout << i << '\n' << res[0] << ' ' << res[1];
            return 0;
        }
    }

    return 0;
}

Compilation message (stderr)

necklace.cpp: In function 'std::array<int, 2> check(int)':
necklace.cpp:83:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::array<int, 3> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   83 |             if (pt == hashes[1].size()) {
      |                 ~~~^~~~~~~~~~~~~~~~~~~
necklace.cpp:93:24: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::array<int, 3> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   93 |                 if (pt == hashes[1].size()) {
      |                     ~~~^~~~~~~~~~~~~~~~~~~

• Subtask 1: 25 / 25
• Subtask 2: 0 / 20
• Subtask 3: 0 / 40