Submission #887826

#	Time	Username	Problem	Language	Result	Execution time	Memory
887826		phong	Palindromes (APIO14_palindrome)	C++17	73 / 100	265 ms	131072 KiB

palindrome

#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,fma")
#pragma GCC optimize("unroll-loops")
#include<bits/stdc++.h>

#define ll long long
const int nmax = 3e5 + 5;
const ll oo = 1e18;
const int lg = 18;
const ll base = 311;
const ll mod = 734065025437;
#define pii pair<int, int>
#define fi first
#define se second
#define debug(a, n) for(int i = 1; i <= n; ++i) cout << a[i] << ' ';
using namespace std;


int n, cur = 0;
string s;
ll pw[nmax];
ll rmq[2][nmax][lg + 1];
int D_odd[nmax];
int D_even[nmax];

void Calc_D_odd() {
    int L = 1;
    int R = 0;
    for(int i = 1 ; i <= n; i++) {
        if(i > R) D_odd[i] = 0;
        else D_odd[i] = min(R - i, D_odd[L + (R - i)]);
        while(i - D_odd[i] - 1 > 0 && i + D_odd[i] + 1 <= n && s[i - D_odd[i] - 1] == s[i + D_odd[i] + 1]) {
            D_odd[i]++;
        }

        if(i + D_odd[i] > R) {
            R = i + D_odd[i];
            L = i - D_odd[i];
        }
    }
}

void Calc_D_even() {
    int L = 1;
    int R = 0;
    for(int i = 1 ; i < n; i++) {
        int j = i + 1;
        if(j > R) D_even[i] = 0;
        else D_even[i] = min(R - j + 1, D_even[L + (R - j)]);
        while(i - D_even[i] > 0 && j + D_even[i] <= n && s[i - D_even[i]] == s[j + D_even[i]]) {
            D_even[i]++;
        }
        if(i + D_even[i] > R) {
            R = i + D_even[i];
            L = j - D_even[i];
        }
    }
}

ll combine(ll a, ll b, int x){
    return (a * pw[x] + b) % mod;
}
void Init(){
    pw[0] = 1;
    for(int i = 1, j; i <= n; ++i){
        pw[i] = pw[i - 1] * base % mod;
        rmq[0][i][0] = s[i] - 'a' + 3;
        rmq[1][i][0] = s[n - i + 1] - 'a' + 3;
    }
    for(int j = 1; j <= lg; ++j){
        for(int i = 1; i + (1 << j) - 1 <= n; ++i){
            for(int t = 0; t < 2; ++t){
                rmq[t][i][j] = combine(rmq[t][i][j - 1], rmq[t][i + (1 << (j - 1))][j - 1], 1 << (j - 1));
            }
        }
    }
}
ll get(int l, int r, int t){
    int k = r - l + 1;
    ll res = 0;
    for(int j = 0; j <= __lg(k); ++j){
        if(k >> j & 1){
            res = combine(res, rmq[t][l][j], 1 << j);
            l += 1 << j;
        }
    }
    return res;
}

bool check(int l, int r){
    return get(l, r, 0) == get(n - r + 1, n - l + 1, 1);
}

map<ll, bool> mp;
map<ll, int>  ind;
int cnt[nmax];
ll f[nmax];
vector<int> tmp;
vector<int> adj[nmax];

void update(int l, int r){
    bool ok = 1;
    while(l <= r){
        ll x = get(l, r, 0);
        if(!mp[x]){
            ind[x] = ++cur;
            tmp.push_back(cur);
            if(ok){
                f[cur]++;
                ok = 0;
            }
            cnt[cur] = r - l + 1;
            mp[x] = 1;

        }
        else{
            int id = ind[x];
            tmp.push_back(id);
            if(ok) f[id]++;

            break;
        }
        ++l, --r;
    }
    if(l > r) tmp.push_back(0);
    int x = (int)tmp.size() - 1;
    for(int i = 0; i < x; ++i){
        int x = tmp[i], y = tmp[i + 1];
        adj[y].push_back(x);
    }
    tmp.clear();
}
void dfs(int u){
    for(auto v : adj[u]){
        dfs(v);
        f[u] += f[v];
    }
}
main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);cout.tie(0);
//    freopen("code.inp", "r", stdin);
//    freopen("code.out", "w", stdout);
    cin >> s;
    n = s.size(); s = ' ' + s + ' ';
    Init();
    Calc_D_odd();
    Calc_D_even();
    for(int i = 1; i <= n; ++i){
        update(i - D_odd[i], i + D_odd[i]);
        if(i < n) update(i - D_even[i] + 1, i + D_even[i]);
    }
    dfs(0);

    ll ans = 0;
    for(int i = 1; i <= cur; ++i){
        ans = max(ans, 1ll * f[i] * cnt[i]);
    }
    cout << ans;
}
/*

*/

Compilation message (stderr)

palindrome.cpp: In function 'void Init()':
palindrome.cpp:65:20: warning: unused variable 'j' [-Wunused-variable]
   65 |     for(int i = 1, j; i <= n; ++i){
      |                    ^
palindrome.cpp: At global scope:
palindrome.cpp:139:1: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
  139 | main(){
      | ^~~~

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