Submission #880861

#	Time	Username	Problem	Language	Result	Execution time	Memory
880861		vjudge1	Necklace (Subtask 1-3) (BOI19_necklace1)	C++17	5 / 85	84 ms	2176 KiB

necklace

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

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

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 = 229939, M = 1e9 + 9;
const int inv = power(P, M - 2, M);

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

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

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

            int t = j + sz - 1;
            hashes[i].pb({h, n[i] - t - 1});
            for (int k = j + 1; k < j + sz; ++k) {
                h = (h - s[i][k - 1] + M) % M;
                h = 1ll * h * inv % M;
                h = (h + 1ll * s[i][k - 1] * pw[sz - 1]) % M;
                hashes[i].pb({h, 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 [h, idx] : hashes[0]) {
        while (h > hashes[1][pt][0]) {
            ++pt;
            if (pt == hashes[1].size()) {
                return {-1, -1};
            }
        }
        if (hashes[1][pt][0] == h) {
            return {idx, hashes[1][pt][1]};
        }
    }
    return {-1, -1};
}

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

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

    cin >> s[0] >> s[1];
    n[0] = s[0].size();
    n[1] = s[1].size();
    
    int l = 0, r = min(n[0], n[1]) + 1, m;
    while (r - l > 1) {
        m = (l + r) / 2;
        pii res = check(m);
        pii neg = {-1, -1};
        if (res != neg) {
            l = m;
        }
        else {
            r = m;
        }
    }

    if (l == 0) {
        while (true) {
        
        }
    }

    cout << l << '\n';
    pii ans = check(l);
    cout << ans[0] << ' ' << ans[1];

    return 0;
}

Compilation message (stderr)

necklace.cpp: In function 'std::array<int, 2> check(int)':
necklace.cpp:71:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::array<int, 2> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   71 |             if (pt == hashes[1].size()) {
      |                 ~~~^~~~~~~~~~~~~~~~~~~

• Subtask 1: 5 / 25
• Subtask 2: 0 / 20
• Subtask 3: 0 / 40