Submission #534686

#	Time	Username	Problem	Language	Result	Execution time	Memory
534686		alextodoran	Palindromic Partitions (CEOI17_palindromic)	C++17	100 / 100	125 ms	24700 KiB

palindromic

/**
 ____ ____ ____ ____ ____
||a |||t |||o |||d |||o ||
||__|||__|||__|||__|||__||
|/__\|/__\|/__\|/__\|/__\|

**/

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int N_MAX = 1000000;

const int MOD = (int) 1e9 + 7;

int pwr (const int &a, const int &b) {
    if (b == 0) {
        return 1;
    } else if (b & 1){
        return (ll) a * pwr(a, (b ^ 1)) % MOD;
    } else {
        int aux = pwr(a, (b >> 1));
        return (ll) aux * aux % MOD;
    }
}
int inv (const int &a) {
    return pwr(a, MOD - 2);
}

int n;
string s;

int pw[N_MAX + 2];
int ipw[N_MAX + 2];
void precalc () {
    pw[0] = 1; pw[1] = 26;
    ipw[0] = 1; ipw[1] = inv(26);
    for (int i = 2; i < N_MAX; i++) {
        pw[i] = (ll) pw[i - 1] * pw[1] % MOD;
        ipw[i] = (ll) ipw[i - 1] * ipw[1] % MOD;
    }
}

int pref[N_MAX + 2];
void init () {
    for (int i = 1; i <= n; i++) {
        pref[i] = (pref[i - 1] + (ll) pw[i - 1] * (int) (s[i] - 'a')) % MOD;
    }
}
int query (int l, int r) {
    return (ll) (pref[r] - pref[l - 1] + MOD) * ipw[l - 1] % MOD;
}

int main () {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    precalc();

    int t;
    cin >> t;
    while (t--) {
        cin >> s; n = (int) s.size();
        s = " " + s;
        init();
        int answer = 1;
        int l1 = 1, r1 = 1;
        int l2 = n, r2 = n;
        while (r1 < l2) {
            if (query(l1, r1) == query(l2, r2)) {
                answer += 2;
                if (l2 - r1 == 1) {
                    answer -= 1;
                }
                l1 = r1 = r1 + 1;
                l2 = r2 = l2 - 1;
            } else {
                r1++;
                l2--;
            }
        }
        cout << answer << "\n";
    }

    return 0;
}

• Subtask 1: 15 / 15
• Subtask 2: 20 / 20
• Subtask 3: 25 / 25
• Subtask 4: 40 / 40