Submission #982706

#	Time	Username	Problem	Language	Result	Execution time	Memory
982706		vjudge1	Palindromic Partitions (CEOI17_palindromic)	C++17	100 / 100	278 ms	55008 KiB

palindromic

#include <bits/stdc++.h>
#define pii pair<int,int>
#define int long long
#define ff first
#define ss second
using namespace std;
const int mod = 1e9 + 7;
const int p1 = 97;
const int p2 = 107;
const int binv = 268041239;
const int binv2 = 224299067;
const int maxn = 1e6;
vector<int> pows(maxn+7,1);
vector<int> invs(maxn+7,1);
vector<int> pows2(maxn+7,1);
vector<int> invs2(maxn+7,1);
void init()
{
    for (int i = 1; i < maxn; i++)
        pows[i] = pows[i-1]*p1%mod;
    for (int i = 1; i < maxn; i++)
        invs[i] = invs[i-1]*binv%mod;
        
    for (int i = 1; i < maxn; i++)
        pows2[i] = pows2[i-1]*p2%mod;
    for (int i = 1; i < maxn; i++)
        invs2[i] = invs2[i-1]*binv2%mod;
    
}

void solve()
{
    
    string s;
    cin >> s;
    int n = s.length();
    vector<int> dp(n/2+2,0);
    int back = n-1;
    vector<int> hash(n);
    hash[0] = s[0]*pows[0]%mod;
    for (int i = 1; i < n; i++)
    {
        hash[i] = hash[i-1] + (s[i]*pows[i]%mod);
        hash[i] %= mod;
    }
    vector<int> hash2(n);
    hash2[0] = s[0]*pows2[0]%mod;
    for (int i = 1; i < n; i++)
    {
        hash2[i] = hash2[i-1] + (s[i]*pows2[i]%mod);
        hash2[i] %= mod;
    }
    auto mile = [&](int i,int j)
    {
        pii base = {hash[j],hash2[j]};
        if (i > 0)
        {
            base.ff-=hash[i-1]-2*mod;
            base.ss-=hash2[i-1]-2*mod;
            base.ff%=mod;
            base.ss%=mod;
            base.ff*=invs[i];
            base.ss*=invs2[i];
            base.ff%=mod;
            base.ss%=mod;
        }
        return ((pii)base);
        
    };
    int lst = 0;
    for (int i = 0; i < n/2+1; i++)
    {
        if (i >= back)
            break;
        
            //cout << s.substr(j,i-j+1) << ' ' << s.substr(back,i-j+1) << " i: " << i << " j: " << j << '\n';
            pii alpha = mile(lst,i);
            pii sigma = mile(back,back+(i-lst));
            if (alpha == sigma)
            {
                if (lst==0)
                    dp[i] = max(dp[i],2ll);
                else if (dp[lst-1] > 0)
                    dp[i] = max(dp[i],dp[lst-1]+2);
                lst = i+1;
            }
        
        back--;
    }
    int ans = 1;
    if (n%2)
    {
        for (int i = 0; i < n/2+1; i++)
        {
            ans = max(ans,dp[i]+1);   
        }
    }
    else
    {
        for (int i = 0; i < n/2-1; i++)
        {
            ans = max(ans,dp[i]+1);
        }
        ans = max(ans,dp[n/2-1]);
    }
    cout << ans << '\n';
}

signed main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    int t;
    cin >> t;
    init();
    while(t--)
    {
       solve();
    }
    
    
    return 0;
}

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