Submission #928925

#	Time	Username	Problem	Language	Result	Execution time	Memory
928925		Ghulam_Junaid	Necklace (Subtask 1-3) (BOI19_necklace1)	C++17	5 / 85	7 ms	1628 KiB

necklace

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

typedef long long ll;

const ll base = 727;
const ll mod = 1e9 + 9;
const ll N = 3005;

unordered_map<ll, ll> ind;
pair<ll, ll> ans[N];
ll pwr[N];

int main(){
    pwr[0] = 1;
    for (ll i = 1; i < N; i ++)
        pwr[i] = (1ll * base * pwr[i - 1]) % mod;

    string s, t;
    cin >> s >> t;

    ll n = s.size();
    ll m = t.size();

    for (ll i = 0; i < m; i ++){
        ll hash = 0;
        for (ll j = i; j < m; j ++){
            hash = (1ll * base * hash + t[j]) % mod;
            ind[hash] = i;
        }
    }

    ll l = 0;
    ll r = n + 1;

    while (r - l > 1){
        ll len = (l + r) / 2;
        bool good = 0;

        for (ll i = 0; i + len - 1 < n; i ++){
            ll hash = 0;
            for (ll j = i; j < i + len; j ++)
                hash = (1ll * base * hash + s[j]) % mod;
            
            if (ind.find(hash) != ind.end()){
                ans[len] = {i, ind[hash]};
                good = 1;
                break;
            }
            for (ll j = i; j < i + len - 1; j ++){
                hash = (-(1ll * s[j] * pwr[len - 1]) + hash) % mod;
                hash += mod;
                hash %= mod;

                hash = (1ll * hash * base + s[j]) % mod;
                if (ind.find(hash) != ind.end()){
                    ans[len] = {i, ind[hash]};
                    good = 1;
                    break;
                }
            }

            if (good) break;
        }

        if (good)
            l = len;
        else
            r = len;
    }

    assert(l > 0);

    vector<pair<ll, pair<ll, ll>>> save;
    save.push_back({l, ans[l]});

    reverse(s.begin(), s.end());

    l = 0;
    r = n + 1;

    while (r - l > 1){
        ll len = (l + r) / 2;
        bool good = 0;

        for (ll i = 0; i + len - 1 < n; i ++){
            ll hash = 0;
            for (ll j = i; j < i + len; j ++)
                hash = (1ll * base * hash + s[j]) % mod;
            
            if (ind.find(hash) != ind.end()){
                ans[len] = {i, ind[hash]};
                good = 1;
                break;
            }
            for (ll j = i; j < i + len - 1; j ++){
                hash = (-(1ll * s[j] * pwr[len - 1]) + hash) % mod;
                hash += mod;
                hash %= mod;

                hash = (1ll * hash * base + s[j]) % mod;
                if (ind.find(hash) != ind.end()){
                    ans[len] = {i, ind[hash]};
                    good = 1;
                    break;
                }
            }

            if (good) break;
        }

        if (good)
            l = len;
        else
            r = len;
    }

    assert(l > 0);

    save.push_back({l, {n - (l + ans[l].first - 1) - 1, ans[l].second}});
    sort(save.begin(), save.end());

    pair<ll, ll> output = save[1].second;
    cout << save[1].first << endl;
    cout << output.first << " " << output.second << endl;
}

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