Submission #299284

#	Time	Username	Problem	Language	Result	Execution time	Memory
299284		AaronNaidu	Palindromes (APIO14_palindrome)	C++14	8 / 100	1035 ms	2204 KiB

palindrome

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

ll mod1 = 1000000009;
string s;
ll n;
ll prefSums[20000], sufSums[20000];
ll pows[20000];
unordered_map<ll, ll> m;

ll divide1(ll num, ll den) {
    while (num < 0)
    {
        num += mod1;
    }
    while (den < 0)
    {
        den += mod1;
    }
    ll inv = 1;
    ll exp = den;
    exp %= mod1;
    for (int i = 0; i < 32; i++)
    {
        if ((mod1-2) & (1<<i))
        {
            inv *= exp;
            inv %= mod1;
        }
        exp *= exp;
        exp %= mod1;
    }
    ll ans = num * inv;
    ans %= mod1;
    return ans;
}


int main() {
    cin >> s;
    ll thisPow = 1;
    n = s.length();
    for (int i = 0; i < n; i++)
    {
        pows[i]= thisPow;
        thisPow *= 11;
        thisPow %= mod1;
    }
    prefSums[0] = s[0] - 'a' + 1;
    for (int i = 1; i < n; i++)
    {
        prefSums[i] = prefSums[i-1] + (s[i] - 'a' + 1) * pows[i];  
        prefSums[i] %= mod1;  
    }
    sufSums[n-1] = s[n-1] - 'a' + 1;
    for (int i = n-2; i >= 0; i--)
    {
        sufSums[i] = sufSums[i+1] + (s[i] - 'a' + 1) * pows[n-1-i];
        sufSums[i] %= mod1;
    }

    ll totMax = 0;
    for (int j = 0; j < n-1; j++)
    {
        if (prefSums[j] == divide1(sufSums[0]-sufSums[j+1], pows[n-1-j]))
        {
            ll curr = 0;
            auto z = m.find(prefSums[j]);
            if (z != m.end())
            {
                curr =z->second;
                m.erase(z);
            }
            curr += j+1;   
            totMax = max(totMax, curr);
            m.insert({prefSums[j], curr});
        }
    }
    if (prefSums[n-1] == sufSums[0])
    {
        ll curr = 0;
        auto z = m.find(prefSums[n-1]);
        if (z != m.end())
        {
            curr =z->second;
            m.erase(z);
        }
        curr += n;
        totMax = max(totMax, curr);
        m.insert({prefSums[n-1], curr});
    }
    for (int i = 1; i < n; i++)
    {
        for (int j = i; j < n-1; j++)
        {
            if (divide1(prefSums[j]-prefSums[i-1], pows[i]) == divide1(sufSums[i]-sufSums[j+1], pows[n-1-j]))
            {            
                ll curr = 0;
                auto z = m.find(divide1(prefSums[j]-prefSums[i-1], pows[i]));
                if (z != m.end())
                {
                    curr = z->second;
                    m.erase(z);
                }
                curr += j-i+1;
                totMax = max(totMax, curr);
                m.insert({divide1(prefSums[j]-prefSums[i-1], pows[i]), curr});
            }
        }
        if (divide1(prefSums[n-1]-prefSums[i-1], pows[i]) == sufSums[i])
        {
            ll curr = 0;
            auto z = m.find(sufSums[i]);
            if (z != m.end())
            {
                curr = z->second;
                m.erase(z);
            }
            curr += n-i;
            totMax = max(totMax, curr);
            m.insert({sufSums[i], curr});
        }
    }
    cout << totMax << "\n";
}

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