Submission #564958

#	Time	Username	Problem	Language	Result	Execution time	Memory
564958		ac2hu	Palindromes (APIO14_palindrome)	C++14	47 / 100	1094 ms	79440 KiB

palindrome

#include <bits/stdc++.h>
#ifdef DEBUG
#include "../templates/debug.h"
#else 
#define deb(x...)
#endif
using namespace std;
typedef unsigned long long ull;
 
// Generate random base in (before, after) open interval:
int gen_base(const int before, const int after) {
    auto seed = std::chrono::high_resolution_clock::now().time_since_epoch().count();
    std::mt19937 mt_rand(seed);
    int base = std::uniform_int_distribution<int>(before+1, after)(mt_rand);
    return base % 2 == 0 ? base-1 : base;
}
 
struct PolyHash {/*{{{*/
    // -------- Static variables --------
    static const int mod = (int)1e9+123; // prime mod of polynomial hashing
    static std::vector<int> pow1;        // powers of base modulo mod
    static std::vector<ull> pow2;        // powers of base modulo 2^64
    static int base;                     // base (point of hashing)
 
    // --------- Static functons --------
    static inline int diff(int a, int b) { 
        // Diff between `a` and `b` modulo mod (0 <= a < mod, 0 <= b < mod)
        return (a -= b) < 0 ? a + mod : a;
    }
 
    // -------------- Variables of class -------------
    std::vector<int> pref1; // Hash on prefix modulo mod
    std::vector<ull> pref2; // Hash on prefix modulo 2^64
 
    // Cunstructor from string:
    PolyHash(const std::string& s)
        : pref1(s.size()+1u, 0)
        , pref2(s.size()+1u, 0)
    {
        assert(base < mod);
        const int n = s.size(); // Firstly calculated needed power of base:
        while ((int)pow1.size() <= n) {
            pow1.push_back(1LL * pow1.back() * base % mod);
            pow2.push_back(pow2.back() * base);
        }
        for (int i = 0; i < n; ++i) { // Fill arrays with polynomial hashes on prefix
            assert(base > s[i]);
            pref1[i+1] = (pref1[i] + 1LL * s[i] * pow1[i]) % mod;
            pref2[i+1] = pref2[i] + s[i] * pow2[i];
        }
    }
 
    // Polynomial hash of subsequence [pos, pos+len)
    // If mxPow != 0, value automatically multiply on base in needed power. Finally base ^ mxPow
    inline std::pair<int, ull> operator()(const int pos, const int len, const int mxPow = 0) const {
        int hash1 = pref1[pos+len] - pref1[pos];
        ull hash2 = pref2[pos+len] - pref2[pos];
        if (hash1 < 0) hash1 += mod;
        if (mxPow != 0) {
            hash1 = 1LL * hash1 * pow1[mxPow-(pos+len-1)] % mod;
            hash2 *= pow2[mxPow-(pos+len-1)];
        }
        return std::make_pair(hash1, hash2);
    }
};/*}}}*/
int PolyHash::base((int)1e9 + 7);
vector<int> PolyHash::pow1{1};
vector<ull> PolyHash::pow2{1};
const int C = 26;
struct node{
    int child[C];
    int cnt = 0;
    int dist = 0;
};
node root1[(int)3e5], root2[(int)3e5];
int r1 = 1, r2 = 1;
void make_node_r1(int id, int d){
    for(int i = 0;i<C;i++){
        root1[id].child[i] = 0;
    }
    root1[id].cnt = 0;
    root1[id].dist = d;
}
void make_node_r2(int id, int d){
    for(int i = 0;i<C;i++){
        root2[id].child[i] = 0;
    }
    root2[id].cnt = 0;
    root2[id].dist = d;
}
string s;
int ans = 1;
void add1(int l,int r){
    int val = 1;
    for(int i = l;i<=r;i++){
        int c = s[i] - 'a';
        if(!root1[val].child[c]){
            root1[val].child[c] = ++r1;
            make_node_r1(root1[val].child[c], root1[val].dist + 2);
        }
        val= root1[val].child[c];
        ++root1[val].cnt;
        ans = max(ans, root1[val].cnt*root1[val].dist);
    }
}
void add2(int l,int r){
    int val = 1;
    for(int i = l;i<=r;i++){
        int c = s[i] - 'a';
        if(!root2[val].child[c]){
            root2[val].child[c] = ++r2;
            make_node_r2(root2[val].child[c], root2[val].dist + 2);
        }
        val= root2[val].child[c];
        ++root2[val].cnt;
        ans = max(ans, root2[val].cnt*root2[val].dist);
    }
}
signed main(){
    make_node_r1(1,-1);
    make_node_r2(1,0);
    cin >> s;
    string r = s;
    reverse(r.begin(), r.end());
    int n = s.size();
    PolyHash nor(s);
    PolyHash rev(r);
    auto is_pali = [&](int l,int r){
        int siz = (r - l + 1);
        if(siz%2 == 0){
            int m = (l + r)/2;
            // (i,m) == rev(m + 1, r)
            auto g = nor(l,m - l + 1, n);
            auto l = rev(n - r - 1, r - m, n);
            return (g == l);
        }
        else{
            int m = (l + r)/2;
            auto g = nor(l,m - l, n);
            auto l = rev(n - r - 1, r -m, n);
            return (g == l);
        }
    };
    vector<int> leq(n,0);
    vector<int> req(n,0);
    for(int i = 1;i<n;i++){
        if(s[i] == s[i - 1])leq[i] = 1 + leq[i - 1];
    }
    for(int i = n - 2;i>=0;i--){
        if(s[i] == s[i + 1])req[i] = 1 + req[i + 1];
    }
    for(int i = 0;i<n;i++){
        auto check = [&](int mid)->bool{
            if(i - mid < 0)return false;
            if(i + mid > n - 1)return false;
            return is_pali(i - mid, i + mid);
        };
        int l = min(leq[i], req[i]) + 1,r = n - 1;
        if(l <= r && check(l)){
            while(l < r){
                int mid = (l + r + 1)/2;
                if(check(mid))
                    l = mid;
                else
                    r = mid - 1;
            }
            add1(i,i + l);
        }
        if(i > 0 && s[i] == s[i - 1]){
            l = min(leq[i - 1], req[i]) + 1,r = n - 1;
            if(l <= r && i - 1 - l >=0 && i + l < n && is_pali(i - 1 - l,i + l)){
                while(l < r){
                    int mid = (l + r + 1)/2;
                    if(i - 1 - mid >=0 && i + mid < n && is_pali(i - 1 - mid, i + mid)){
                        l = mid;
                    }
                    else
                        r = mid - 1;
                }
                add2(i,i + l);
            }
        }
    }
    vector<vector<int>> temp(26);
    for(int i = 0;i<n;i++){
        temp[s[i] - 'a'].push_back(req[i] + 1);
    }
    for(int j = 0;j<26;j++){
        vector<int> cc(n + 2, 0);
        for(auto e : temp[j]){
            cc[e + 1]--;
            cc[0]++;
        }
        for(int i = 1;i<=n + 1;i++)cc[i] += cc[i - 1];
        for(int i = 0;i<=n;i++){
            ans = max(ans, cc[i]*i);
        }
    }
    cout << ans << "\n";
}

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