Submission #677933

#	Time	Username	Problem	Language	Result	Execution time	Memory
677933		Romiros	Palindromes (APIO14_palindrome)	C++17	100 / 100	954 ms	59676 KiB

palindrome

#include <bits/stdc++.h>
 
#define ll long long
#define ld long double
#define vi vector<int>
#define pii pair<int, int>
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
 
#pragma GCC optimize("O3", "unroll-loops")
#pragma GCC target("avx2", "popcnt")

using namespace std;
 
const int MAXN = 3e5 + 10;
 
inline vector<int> build_sa(string s){
    s+='$';
    int n= s.size();
    vector<int>p(n),pn(n),cn(n),c(n),cnt(n);
    {
        vector<pii>a(n);
        for(int i=0;i<n;i++) a[i]={s[i]-'a',i};
        sort(all(a));
        for(int i=0;i<n;i++) p[i]=a[i].second;
        c[p[0]]=0;
        for(int i=1;i<n;i++){
            if(a[i].first ==a[i-1].first ){
                c[p[i]]=c[p[i-1]];
            }
            else{
                c[p[i]]=c[p[i-1]]+1;
            }
        }
    }
    int k=0;
    while((1 << k)<n){
        cnt.assign(n,0);
        for(int i=0;i<n;i++){
            pn[i]=p[i]-(1 << k);
            if(pn[i]<0) pn[i]+=n;
        }
        for(auto &z : c) cnt[z]++;
        for(int i=1;i<n;i++) cnt[i]+=cnt[i-1];
        for(int i=n-1;i>=0;i--){
            --cnt[c[pn[i]]];
            p[cnt[c[pn[i]]]]=pn[i];
        }
        cn[p[0]]=0;
        for(int i=1;i<n;i++){
            int f=(p[i]+(1 << k))%n,s=(p[i-1]+(1 << k))%n;
            if(c[p[i]]!=c[p[i-1]] || c[f]!=c[s]){
                cn[p[i]]=cn[p[i-1]]+1;
            }else cn[p[i]]=cn[p[i-1]];
        }
        c=cn;
        k++;
    }
    return p;
}
 
inline vector<int> build_lcp(const vector<int>& p, const string& s){
    int n = s.size();
    vector<int> pos(n + 1);
    for (int i = 0; i <= n; i++){
        pos[p[i]] = i;
    }
    vector<int> lcp(n);
    int k = 0;
    for (int i = 0; i < (n - 1); i++){
        while (s[i + k] == s[p[pos[i] - 1] + k]){
            k++;
        }
        lcp[pos[i] - 1] = k;
        k -= (k != 0);
    }
    return lcp;
}

struct SparseTable{
    vector<vector<int>> st;

    SparseTable(vector<int> a){
        int n = a.size();
        st.resize(n);
        for (int i = 0; i < n; i++){
            st[i].push_back(a[i]);
        }
        for (int k = 1; k <= n; k *= 2){
            for (int i = 0; i + k < n; i++){
                st[i].push_back(min(st[i].back(), st[i + k].back()));
            }
        }
    }

    inline int log2(int x){
        return 31 - __builtin_clz(x);
    }

    inline int get(int l, int r){
        if (l > r){
            return 1e9;
        }
        int k = log2(r - l + 1);
        return min(st[l][k], st[r - (1 << k) + 1][k]);
    }
};

SparseTable sp({});
vector<int> d(MAXN);
vector<int> pos;
string s;

inline int lcp(int i, int j){
    int l = pos[i];
    int r = pos[j];
    if (l > r){
        swap(l, r);
    }
    return min({d[i], d[j], sp.get(l, r - 1)});
}

inline int cmp(int i, int j){
    int l = lcp(i, j);
    if (l == min(d[i], d[j])){
        return d[i] < d[j];
    }
    return s[i - l] < s[j - l];
}

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    #ifdef ON_PC
        freopen("input.txt", "r", stdin);
    #endif
    // freopen("output.txt", "w", stdout);
    int T = 1;
    // cin >> T;
    while (T--){
        cin >> s;
        int n = s.size();   
        vector<int> sa = build_sa(s);
        vector<int> lcpv = build_lcp(sa, s);
        pos = vector<int>(n + 2);
        for (int i = 0; i < sa.size(); i++){
            pos[sa[i] + 1] = i;
        }
        sp = SparseTable(lcpv);
        s = " " + s;
        ll res = 0;
        vector<int> order(n);
        vector<int> lb(n);
        vector<int> rb(n);
        vector<int> st;
        vector<int> lcp_res(n);
        for (int f = 0; f < 2; f++){
            d.assign(n + 1, 0);
            for (int i = 1, l = 0, r = -1; i <= n; i++){
                if (i + f <= r){
                    d[i] = min(r - (i + f) + 1, d[l + r - (i + f)]);
                }
                while (i - d[i] >= 1 && i + f + d[i] <= n && 
                       s[i - d[i]] == s[i + f + d[i]]){
                           d[i]++;
                }
                if (i + f + d[i] - 1 > r){
                    r = i + f + d[i] - 1;
                    l = i - d[i] + 1;
                }
            }
            for (int i = 1; i <= n; i++){
                res = max(res, (ll)(2 * d[i] - !f));
            }
            for (int i = 1; i <= n; i++){
                order[i - 1] = i;
            }
            sort(all(order), cmp);
            for (int i = 0; i + 1 < n; i++){
                lcp_res[i] = lcp(order[i], order[i + 1]);
            }
            for (int i = 0; i < n; i++){
                while (!st.empty() && lcp_res[st.back()] >= lcp_res[i]){
                    st.pop_back();
                }
                lb[i] = 0;
                if (!st.empty()){
                    lb[i] = st.back() + 1;
                }
                st.push_back(i);
            }
            st.clear();
            for (int i = n - 1; i >= 0; i--){
                while (!st.empty() && lcp_res[st.back()] >= lcp_res[i]){
                    st.pop_back();
                }
                rb[i] = n - 1;
                if (!st.empty()){
                    rb[i] = st.back();
                }
                st.push_back(i);
            }
            st.clear();
            for (int i = 0; i < n; i++){
                res = max(res, (2 * lcp_res[i] - !f) * 1ll * (rb[i] - lb[i] + 1));
            }
        }
        cout << res << "\n";
    }
    return 0;
}

Compilation message (stderr)

palindrome.cpp: In function 'int main()':
palindrome.cpp:147:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  147 |         for (int i = 0; i < sa.size(); i++){
      |                         ~~^~~~~~~~~~~

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