Submission #122362

#	Time	Username	Problem	Language	Result	Execution time	Memory
122362		BThero	Palindromic Partitions (CEOI17_palindromic)	C++17	100 / 100	166 ms	17152 KiB

palindromic

// Why am I so dumb? :c
// chrono::system_clock::now().time_since_epoch().count()

//#pragma GCC optimize("Ofast")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

#include<bits/stdc++.h>
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>

#define pb push_back
#define mp make_pair

#define all(x) (x).begin(), (x).end()

#define fi first
#define se second

using namespace std;
using namespace __gnu_pbds;

typedef long long ll;   
typedef pair<int, int> pii;
template<typename T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

const int MAXN = (int)1e6 + 5;
const int INF = (int)1e9;
const int MOD = (int)1e9 + 7;
const int MOD2 = (int)1e9 + 9;
const int P = 31;
const int P2 = 37;

int pref[MAXN], pref2[MAXN];

int PW[MAXN], PW2[MAXN];

char s[MAXN];

int n, ans;

int addMod(int a, int b, int m) {
    a += b;

    if (m <= a) {
        a -= m;
    }

    return a;
}

int mulMod(int a, int b, int m) {
    return a * 1ll * b % m;
}

void pre() {
    PW[0] = 1;
    PW2[0] = 1;

    for (int i = 1; i < MAXN; ++i) {
        PW[i] = mulMod(PW[i - 1], P, MOD);
        PW2[i] = mulMod(PW2[i - 1], P2, MOD2);
    }
}

bool good(int l, int r) {
    int l2 = n - r + 1;
    int r2 = n - l + 1;

    int a1 = addMod(pref[r], MOD - pref[l - 1], MOD);
    int a2 = addMod(pref2[r], MOD2 - pref2[l - 1], MOD2);

    int b1 = addMod(pref[r2], MOD - pref[l2 - 1], MOD);
    int b2 = addMod(pref2[r2], MOD2 - pref2[l2 - 1], MOD2);

    a1 = mulMod(a1, PW[n - l], MOD);
    a2 = mulMod(a2, PW2[n - l], MOD2);
    b1 = mulMod(b1, PW[n - l2], MOD);
    b2 = mulMod(b2, PW2[n - l2], MOD2);

    return a1 == b1 && a2 == b2;
}

void solve() {
    scanf("%s", s + 1);         
    for (n = 1; s[n]; ++n);     

    --n;
    ans = 0;

    for (int i = 1; i <= n; ++i) {
        pref[i] = addMod(pref[i - 1], mulMod(s[i] - 'a' + 1, PW[i], MOD), MOD);
        pref2[i] = addMod(pref2[i - 1], mulMod(s[i] - 'a' + 1, PW2[i], MOD2), MOD2);
    }    

    for (int l = 1, r; l <= n; l = r + 1) {
        r = l;

        while (r * 2 <= n && !good(l, r)) {
            ++r;
        }

        if (r * 2 > n) {
            ++ans;
            break;            
        }

        ans += 2;

        if (r * 2 == n) {
            break;
        }                               
    }    

    printf("%d\n", ans);
}

int main() {
    int tt;
    scanf("%d", &tt);
    
    pre();

    while (tt--) {
        solve();
    }

    return 0;
}

Compilation message (stderr)

palindromic.cpp: In function 'void solve()':
palindromic.cpp:84:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%s", s + 1);         
     ~~~~~^~~~~~~~~~~~~
palindromic.cpp: In function 'int main()':
palindromic.cpp:119:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &tt);
     ~~~~~^~~~~~~~~~~

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