Submission #982696

#	Time	Username	Problem	Language	Result	Execution time	Memory
982696		vjudge1	Palindromic Partitions (CEOI17_palindromic)	C++17	100 / 100	347 ms	39012 KiB

palindromic

#include <bits/stdc++.h>
#define int long long

using namespace std;

int n, M = 1e9+7, P = 31, N = 1e6 + 1;
string s;
vector<int> p, inv, haah;

int mod(int i) {
    return (i + M) % M;
}
int fast(int i, int j) {
    //cout << i << " " << j << "\n";
    if(j == 0) return 1;
    int a = fast(i, j / 2);
    return mod(mod(a * a) * (j % 2 == 0 ? 1 : i));
}

signed main() {
    int t;
    cin >> t;
    //
    p = vector<int>(N), inv = vector<int>(N);
    p[0] = 1;
    for(int i = 1; i < N; i++) p[i] = mod(p[i - 1] * P);
    inv[N - 1] = fast(p[N - 1], M - 2);
    for(int i = N - 2; i > -1; i--) inv[i] = mod(inv[i + 1] * P);
    //
    while(t--) {
        cin >> s;
        n = s.size(), haah = vector<int>(n);
        for(int i = 0; i < n; i++) {
            haah[i] = mod((s[i] - 'a') * p[i]);
            if(i != 0) haah[i] = mod(haah[i - 1] + haah[i]);
            //cout << haah[i] << " ";
        }
        //
        int res = 0, last = 0, a, b;
        bool flag = false;
        for(int i = 0; i < n / 2; i++) {
            a = mod(haah[i] - (last == 0 ? 0 : haah[last - 1]));
            a = mod(a * inv[last]);
            b = mod(haah[n - last - 1] - (n - i - 2 < 0 ? 0 : haah[n - i - 2]));
            b = mod(b * inv[n - i - 1]);
            //
            /*a = 0;
            for(int j = last; j < i + 1; j++) {
                a = mod(a + mod((s[j] - 'a') * p[j - last]));
            }
            //
            b = 0;
            for(int j = n - i - 1; j < n - last; j++) {
                b = mod(b + mod((s[j] - 'a') * p[j - (n - i - 1)]));
            }*/
            //
            //cout << last << " " << i << " " << a << "  1\n";
            //cout << n - i - 1 << " " << n - last - 1 << " " << b << "  2\n";
            if(a == b) {
                res += 2;
                last = i + 1;
            } else if(i == n / 2 - 1) {
                res++;
                flag = true;
            }
        }
        if(!flag && n % 2 == 1) res++;
        //
        cout << res << "\n";
    }
}

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