Submission #164875

#	Time	Username	Problem	Language	Result	Execution time	Memory
164875		godwind	Palindromes (APIO14_palindrome)	C++14	0 / 100	41 ms	25688 KiB

palindrome

#pragma GCC optimize("Ofast")
#pragma GCC optimize("no-stack-protector")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("fast-math")
#pragma GCC target("sse,sse2,sse3,ssse3,popcnt,abm,mmx,tune=native")
#include <iostream>
#include <vector>
#include <algorithm>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <stdio.h>
#include <cstdio>
#include <math.h>
#include <cmath>
#include <string>
#include <cstring>
#include <queue>
#include <deque>
#include <random>
#include <iomanip>
#include <bitset>
#include <cassert>

using namespace std;

#define int long long
#define less less228
#define left left228
#define right right228

template<typename T> void uin(T &a, T b) {
    if (b < a) a = b;
}
template<typename T> void uax(T &a, T b) {
    if (b > a) a = b;
}


random_device rnd;

template<typename T> void shuffle(vector< T > &v) {
    for (int i = 1; i < (int)v.size(); ++i) {
        swap(v[rnd() % i], v[i]);
    }
    for (int i = (int)v.size() - 1; i; --i) {
        swap(v[rnd() % i], v[i]);
    }
}

const int N = 100 * 1000 + 228;
const int BASE = 141, MOD = 2286661337;
const int INF = 1e9 + 228;

int mod(int x) {
    x %= MOD;
    if (x < 0) x += MOD;
    return x;
}

vector<int> get_suffmas(string s) {
    s += '$';
    int n = (int)s.size();
    vector<int> p(n), c(n), cnt(max(256LL, n));
    for (int i = 0; i < n; ++i) {
        ++cnt[(int)s[i]];
    }
    for (int i = 1; i < (int)cnt.size(); ++i) {
        cnt[i] += cnt[i - 1];
    }
    for (int i = 0; i < n; ++i) {
        p[--cnt[(int)s[i]]] = i;
    }
    c[p[0]] = 0;
    for (int i = 1; i < n; ++i) {
        c[p[i]] = c[p[i - 1]];
        if (s[p[i]] != s[p[i - 1]]) ++c[p[i]];
    }
    for (int d = 0; (1 << d) < n; ++d) {
        vector<int> pp(n), cc(n);
        cnt.assign(n, 0);
        for (int i = 0; i < n; ++i) {
            pp[i] = p[i] - (1 << d);
            if (pp[i] < 0) pp[i] += n;
            ++cnt[c[pp[i]]];
        }
        for (int i = 0; i < n; ++i) {
            cnt[i] += cnt[i - 1];
        }
        for (int i = n - 1; i + 1; --i) {
            p[--cnt[c[pp[i]]]] = pp[i];
        }
        cc[p[0]] = 0;
        for (int i = 1; i < n; ++i) {
            cc[p[i]] = cc[p[i - 1]];
            if (c[p[i]] != c[p[i - 1]] || c[(p[i] + (1 << d) % n)] != c[(p[i - 1] + (1 << d)) % n]) {
                ++cc[p[i]];
            }
        }
        c = cc;
    }
    vector<int> ans;
    for (int i : p) {
        if (i != n - 1) {
            ans.push_back(i);
        }
    }
    return ans;
}

vector<int> get_lcp(string s, vector<int> p) {
    int n = (int)s.size();
    vector<int> pos(n), lcp(n - 1);
    for (int i = 0; i < n; ++i) {
        pos[p[i]] = i;
    }
    int k = 0;
    for (int i = 0; i < n; ++i) {
        if (k) --k;
        if (pos[i] == n - 1) {
            k = 0;
        } else {
            int j = p[pos[i] + 1];
            while (max(i, j) + k < n && s[i + k] == s[j + k]) ++k;
            lcp[pos[i]] = k;
        }
    }
    return lcp;
}

int n;
string s;

int go_even[N];
int go_odd[N];
int base[N], h[N], hr[N];
int mx[N], lg[N], st_even[N][20], st_odd[N][20];

int get_hash(int l, int r) {
    return mod(h[r] - h[l - 1] * base[r - l + 1]);
}
int get_rhash(int l, int r) {
    return mod(hr[l] - hr[r + 1] * base[r - l + 1]);
}

void build_sparse() {
    for (int i = 2; i <= n; ++i) {
        lg[i] = lg[i >> 1] + 1;
    }
    for (int i = 1; i <= n; ++i) {
        st_even[i][0] = go_even[i];
        st_odd[i][0] = go_odd[i];
    }
    for (int k = 1; k <= lg[n]; ++k) {
        for (int i = 1; i <= n - (1 << k) + 1; ++i) {
            st_even[i][k] = min(st_even[i][k - 1], st_even[i + (1 << (k - 1))][k - 1]);
            st_odd[i][k] = min(st_odd[i][k - 1], st_odd[i + (1 << (k - 1))][k - 1]);
        }
    }
}

int get_even(int l, int r)
 {
    int k = lg[r - l + 1];
    return min(st_even[l][k], st_even[r - (1 << k) + 1][k]);
}
int get_odd(int l, int r) {
    int k = lg[r - l + 1];
    return min(st_odd[l][k], st_odd[r - (1 << k) + 1][k]);
}

int res = 0;

void pre() {
    base[0] = 1;
    for (int i = 1; i <= n; ++i) {
        base[i] = mod(base[i - 1] * BASE);
    }
    for (int i = 1; i <= n; ++i) {
        h[i] = mod(h[i - 1] * BASE + (int)s[i - 1]);
    }
    for (int i = n; i; --i) {
        hr[i] = mod(hr[i + 1] * BASE + (int)s[i - 1]);
    }

    for (int i = 1; i <= n; ++i) {
        int l = 1, r = min(i, n - i + 1) + 1;
        while (r - l > 1) {
            int mid = (l + r) >> 1;
            if (get_hash(i - mid + 1, i + mid - 1) == get_rhash(i - mid + 1, i + mid - 1)) {
                l = mid;
            } else {
                r = mid;
            }
        }
        go_odd[i] = i - l + 1;
        uax(res, 2 * l - 1);
    }
    for (int i = 1; i <= n; ++i) {
        int l = 1, r = min(i, n - i) + 1;
        while (r - l > 1) {
            int mid = (l + r) >> 1;
            if (get_hash(i - mid + 1, i + mid) == get_rhash(i - mid + 1, i + mid)) {
                l = mid;
            } else {
                r = mid;
            }
        }
        if (i + l <= n && get_hash(i - l + 1, i + l) == get_rhash(i - l + 1, i + l)) {
            go_even[i] = i - l + 1;
            uax(res, 2 * l);
        } else {
            go_even[i] = INF;
        }
    }
    build_sparse();
}

int max_palindrome(int L, int R) {
    ++L, ++R;
    int x = L + (R - L) / 2;
    int l = L, r = x + 1;
    while (r - l > 1) {
        int mid = (l + r) >> 1;
        if (get_odd(mid, x) <= L) {
            l = mid;
        } else {
            r = mid;
        }
    }
    int len = 2 * (l - L + 1) - 1;
    x = L + (R - L - 1) / 2;
    l = L, r = x + 1;
    while (r - l > 1) {
        int mid = (l + r) >> 1;
        if (get_even(mid, x) <= L) {
            l = mid;
        } else {
            r = mid;
        }
    }
    if (l + 1 + (l - L + 1) - 1 <= R && get_even(l, x) <= L) {
        uax(len, 2 * (l - L + 1));
    } else {
        // kekos)))))))))))
    }
    return len;
}


signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cin >> s;
    n = (int)s.size();
    vector<int> p = get_suffmas(s);
    vector<int> lcp = get_lcp(s, p);
    pre();
    vector<int> gol(n), gor(n);
    for (int i = 0; i < n - 1; ++i) {
        gol[i] = -1;
        gor[i] = n - 1;
    }
    vector<int> st;
    for (int i = 0; i < n - 1; ++i) {
        while (!st.empty() && lcp[st.back()] > lcp[i]) {
            gor[st.back()] = i;
            st.pop_back();
        }
        st.push_back(i);
    }
    st.clear();
    for (int i = n - 2; i + 1; --i) {
        while (!st.empty() && lcp[st.back()] > lcp[i]) {
            gol[st.back()] = i;
            st.pop_back();
        }
        st.push_back(i);
    }

    for (int i = 0; i < n - 1; ++i) {
        if (lcp[i] == 0) continue;
        int cnt = gor[i] - gol[i];
        int len = max_palindrome(p[i], p[i] + lcp[i] - 1);
        uax(res, len * cnt);
    }
    cout << res << '\n';
    return 0;

}
// RU_023

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*/

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