Submission #908153

#	Time	Username	Problem	Language	Result	Execution time	Memory
908153		wii	Palindromic Partitions (CEOI17_palindromic)	C++17	60 / 100	33 ms	131076 KiB

palindromic

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

typedef double db;
typedef long long ll;
typedef long double ld;

#define int ll
typedef pair<int, int> pii;

#define lx (id << 1)
#define rx (lx | 1)
#define gcd __gcd
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define bit(i, mask) ((mask) >> (i) & 1)
#define reset(x, val) memset(x, val, sizeof(x))
#define foru(i,a,b) for(int i = (a); i <= (b); ++i)
#define ford(i,a,b) for(int i = (a); i >= (b); --i)
#define FastIO ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);

template<typename T> bool maximize(T &res, const T &val) { if (res < val) { res = val; return true; } return false; }
template<typename T> bool minimize(T &res, const T &val) { if (val < res) { res = val; return true; } return false; }

const ll Linf = 0x3f3f3f3f3f3f3f3f;
const int Inf = 0x3f3f3f3f;
const ll Mod = 1e9 + 7;
const ll Mod2 = ll(1e9) + 9;
const int Lim = 1e6 + 5;
const int inv6 = 166666668;

// #define Sieve
#ifdef Sieve
    vector<int> pr;
    vector<int> lpf;
    void Linear_sieve(int n = Lim) {
        pr.assign(1, 2);
        lpf.assign(n + 1, 2);

        for (int x = 3; x <= n; x += 2) {
            if (lpf[x] == 2) pr.push_back(lpf[x] = x);
            for (int i = 1; i < pr.size() && pr[i] <= lpf[x] && pr[i] * x <= n; ++i)
                lpf[pr[i] * x] = pr[i];
        }
    }
#endif

// #define Ckn_calc
#ifdef Ckn_calc
    const int LIM = 1e6 + 16;

    int fact[LIM + 10]; /// factorial:         fact[n] = n!
    int invs[LIM + 10]; /// inverse modular:   invs[n] = n^(-1)
    int tcaf[LIM + 10]; /// inverse factorial: tcaf[n] = (n!)^(-1)
    void precal_nck(int n = LIM)
    {
        fact[0] = fact[1] = 1;
        invs[0] = invs[1] = 1;
        tcaf[0] = tcaf[1] = 1;
        for (int i = 2; i <= n; ++i)
        {
            fact[i] = (1LL * fact[i - 1] * i) % Mod;
            invs[i] = Mod - 1LL * (Mod / i) * invs[Mod % i] % Mod;
            tcaf[i] = (1LL * tcaf[i - 1] * invs[i]) % Mod;
        }
    }

    ll C(int n, int k) {
        if (n < k || k < 0) return 0;

        ll res = fact[n];
        res *= tcaf[k], res %= Mod;
        res *= tcaf[n - k], res %= Mod;
        return res;
    }

    ll P(int n, int k) {
        ll res = fact[n];
        res *= tcaf[n - k], res %= Mod;
        return res;
    }
#endif

/// ====*====*====*====*====*====*====*====*====*====*====*====*====*====*====*====*====

const int base = 37;
const int N = 1e6 + 5;
const int K = log2(N) + 1;
const int dx[] = {+1, -1, 0, 0};
const int dy[] = {0, 0, +1, -1};
const int block_size = sqrt(2e9) + 2;

int n;
int dp[N];
int nxt[N][26], last[26];
string s;

template<int Mod>
struct HashTable {
    int f[N];
    int w[N];

    void init() {
        w[0] = 1;
        foru(i, 1, n) {
            f[i] = (f[i - 1] * base + (s[i] - 'a' + 1)) % Mod;
            w[i] = (w[i - 1] * base) % Mod;
        }
    }

    int get(int l, int r) {
        return (f[r] - f[l - 1] * w[r - l + 1] % Mod + Mod) % Mod;
    }
};

HashTable<(ll)1e9 + 7> f1;
HashTable<(ll)1e9 + 9> f2;

int ok(int l, int r) {
    return (f1.get(l, r) == f1.get(n - r + 1, n - l + 1)) &&
           (f2.get(l, r) == f2.get(n - r + 1, n - l + 1));
}

void solve() {
	cin >> s;

    n = s.size();
    s = " " + s;

    foru(i, 1, n) dp[i] = -Linf;

    foru(c, 0, 25) last[c] = 0;
    foru(i, 1, n) {
        last[s[i] - 'a'] = i;
        foru(c, 0, 25)
            nxt[i][c] = last[c];
    }

    f1.init();
    f2.init();

    dp[0] = 0;
    foru(i, 1, (n + 1) / 2) {
        int j = n - i + 1;

        while (i <= (n - j + 1) && nxt[j][s[i] - 'a']) {
            j = nxt[j][s[i] - 'a'];

            if (ok(i, n - j + 1)) {
                maximize(dp[n - j + 1], dp[i - 1] + (i <= (n + 1) / 2 && n / 2 < n - j + 1 ? 1 : 2));

                // cout << "? " << i << " " << n - j + 1 << " " << dp[n - j + 1] << "\n";

                i = n - j + 1;
                break;
            }

            // break;

            --j;
        }

        if (i != n - j + 1)
            return cout << 0, void();
    }

    int ans = dp[(n + 1) / 2];
    foru(i, 1, (n + 1) / 2)
        maximize(ans, dp[i - 1] + 1);

    cout << ans << "\n";
}

signed main() {
    FastIO;

    #define task "test"
    if (fopen(task".inp", "r")) {
		freopen(task".inp", "r", stdin);
		freopen(task".out", "w", stdout);
	}

    #ifdef Sieve
        Linear_sieve();
    #endif

    #ifdef Ckn_calc
        precal_nck();
    #endif

    int ntest = 1;
    cin >> ntest;
    while (ntest--) {
        //cout << "Case " << q << ": " << "\n"; 
        solve();
    }

    return 0;
}

/**  /\_/\
 *  (= ._.)
 *  / >TL \>AC
**/

Compilation message (stderr)

palindromic.cpp: In function 'int main()':
palindromic.cpp:179:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  179 |   freopen(task".inp", "r", stdin);
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
palindromic.cpp:180:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  180 |   freopen(task".out", "w", stdout);
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 15 / 15
• Subtask 2: 20 / 20
• Subtask 3: 25 / 25
• Subtask 4: 0 / 40