Submission #676321

#	Time	Username	Problem	Language	Result	Execution time	Memory
676321		vuavisao	Palindromes (APIO14_palindrome)	C++14	23 / 100	1085 ms	8356 KiB

palindrome

#include<bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#define ll long long
using namespace std;

template<typename Lhs, typename Rhs> inline bool Max_self(Lhs &a, Rhs b) { if(b > a) { a = b; return true; } return false; }
template<typename Lhs, typename Rhs> inline bool Min_self(Lhs &a, Rhs b) { if(b < a) { a = b; return true; } return false; }

const int N = 3e5 + 10;

int n;
string s;

namespace sub123 {
    bool check() {
        return n <= 10000;
    }

    const uint8_t size_T = 2;
    const int _1hrd = 100;
    const int _1bil = 1000000000;
    const array<int, size_T> MOD = {_1bil + 9, _1bil + 11};
    const array<int, size_T> BASE = {_1hrd + 28, _1hrd + 31};

    struct Hash {
        array<int, size_T> val = {0};
        Hash() {};
        Hash (int x) {
            for (uint8_t i = 0; i < size_T; ++ i)
                this -> val[i] = x % MOD[i];
        }

        bool operator < (const Hash& other) const {
            for (uint8_t i = 0; i < size_T; ++ i)
                if (this -> val[i] != other.val[i]) return this -> val[i] < other.val[i];
            return false;
        }

        bool operator == (const Hash& other) const {
            for (uint8_t i = 0; i < size_T; ++ i)
                if (this -> val[i] != other.val[i]) return false;
            return true;
        }

        Hash operator + (const int& x) const {
            Hash res;
            for (uint8_t i = 0; i < size_T; ++ i)
                res.val[i] = (1ll * this -> val[i] * BASE[i] + x) % MOD[i];
            return res;
        }

        Hash operator + (const Hash& other) const {
            Hash res;
            for (uint8_t i = 0; i < size_T; ++ i)
                res.val[i] = (this -> val[i] + other.val[i]) % MOD[i];
            return res;
        }

        Hash operator - (const Hash& other) const {
            Hash res;
            for (uint8_t i = 0; i < size_T; ++ i) {
                res.val[i] = (this -> val[i] - other.val[i]) % MOD[i];
                res.val[i] = (res.val[i] + MOD[i]) % MOD[i];
            }
            return res;
        }

        Hash operator * (const Hash& other) const {
            Hash res;
            for (uint8_t i = 0; i < size_T; ++ i)
                res.val[i] = (1ll * this -> val[i] * other.val[i]) % MOD[i];
            return res;
        }

        friend ostream& operator << (ostream& os, Hash& other) {
            os << "[ ";
            for (uint8_t i = 0; i < size_T; ++ i) {
                cout << other.val[i];
                if(i < size_T - 1) cout << ',';
                cout << ' ';
            }
            os << "]";
            return os;
        }
    };

    Hash p[N], h[N], h_rev[N];
    int res;

    Hash get_hash(int l, int r, Hash* h) {
        return h[r] - h[l - 1] * p[r - l + 1];
    }


    void solve() {
        p[0] = 1;
        for(int i = 1; i <= n; ++ i) {
            p[i] = p[i - 1] + 0;
            h[i] = h[i - 1] + s[i];
            h_rev[i] = h_rev[i - 1] + s[n - i + 1];
        }
        for(int len = 1; len <= n; ++ len) {
            vector<Hash> candidates = {};
            auto palin = [&] (int l, int r) -> bool {
                return get_hash(l, r, h) == get_hash(n - r + 1, n - l + 1, h_rev);
            };
            for(int i = 1; i <= n - len + 1; ++ i) {
                if(palin(i, i + len - 1)) candidates.push_back(get_hash(i, i + len - 1, h));
            }
            sort(candidates.begin(), candidates.end());
            for(int i = 0, j = 0; i < (int) candidates.size(); i = j) {
                while(candidates[j] == candidates[i]) ++ j;
                Max_self(res, (j - i) * len);
            }
        }
        cout << res;
    }
}

int32_t main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    if (fopen("APIO14_palindrome.inp", "r")) {
        freopen("APIO14_palindrome.inp", "r", stdin);
        freopen("APIO14_palindrome.out", "w", stdout);
    }
    cin >> s; n = (int) s.size(); s = ' ' + s;
    if(sub123::check()) {
        sub123::solve();
        return 0;
    }
    return 0;
}

/// Code by vuavisao

Compilation message (stderr)

palindrome.cpp: In function 'int32_t main()':
palindrome.cpp:126:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  126 |         freopen("APIO14_palindrome.inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
palindrome.cpp:127:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  127 |         freopen("APIO14_palindrome.out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 8 / 8
• Subtask 2: 15 / 15
• Subtask 3: 0 / 24
• Subtask 4: 0 / 26
• Subtask 5: 0 / 27