Submission #723298

#	Time	Username	Problem	Language	Result	Execution time	Memory
723298		drdilyor	Boarding Passes (BOI22_passes)	C++17	60 / 100	1239 ms	378192 KiB

passes

#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimize("unroll-loops")
#include<bits/stdc++.h>
using namespace std;
using ll = long long;
 
inline ll exp_inv(ll x) {
    return x * (x-1);
}
 
int main() {
    char a = 'A';
    string s; cin >> s;
    const int G = 15;
    int n = s.size();
    if (n == 1) {
        cout << "0\n";
        return 0;
    }

    vector suml(G, vector(G, vector(n, 0ll)));
    vector sumr(G, vector(G, vector(n, 0ll)));
    vector cl(G, vector(n, 0ll));
    vector cr(G, vector(n, 0ll));
    vector ix(G, vector<int>());
    for (int c1 = 0; c1 < G; c1++) {
        for (int c2 = 0; c2 < G; c2++) {
            ll res = 0, cur = 0;
            for (int i = 0; i < n; i++) {
                if (s[i] == c1+a)
                    res += cur;
                else if (s[i] == c2+a)
                    cur++;
                suml[c1][c2][i] = res;
            }
        }
    }
    for (int c1 = 0; c1 < G; c1++) {
        for (int c2 = 0; c2 < G; c2++) {
            ll res = 0, cur = 0;
            for (int i = n-1; i >= 0; i --) {
                if (s[i] == c1+a)
                    res += cur;
                else if (s[i] == c2+a)
                    cur++;
                sumr[c1][c2][i] = res;
            }
        }
    }
    for (int j = 0; j < G; j++) {
        int c = 0;
        for (int i = 0; i < n;i ++) {
            if (s[i] == j+a)
                c++;
            cl[j][i] = c;
        }
    }
    for (int j = 0; j < G; j++) {
        int c = 0;
        for (int i = n-1; i >= 0; i--) {
            if (s[i] == j+a)
                c++;
            cr[j][i] = c;
        }
    }
    for (int i = 0; i < n ;i++) 
        ix[s[i] - a].push_back(i);

    vector memo(1<<G, (ll)1e18);
    memo[(1<<G)-1] = 0;
    for (int used = (1<<G)-1-1; used >= 0; used--) {
        ll& res = memo[used];
        for (int i = 0 ;i < G; i++) {
            if (used&1<<i) continue;

            auto f = [&](int j) {
                ll sum = 0;
                for (int c2 = 0; c2 < G; c2++) {
                    if (used&1<<c2) {
                        if (j) sum += suml[i][c2][j-1];
                        if (j <n-1)sum += sumr[i][c2][j];
                    }
                }
                return sum * 4 + (j < n-1 ? exp_inv(cr[i][j]) : 0) + (j ? exp_inv(cl[i][j-1]) : 0);
            };

            int l = -1, r = (int)ix[i].size()-2;
            while (l < r-1) {
                int m = (l+r) / 2;
                ll a = f(ix[i][m]), b = f(ix[i][m+1]);
                if (a == b) break;
                else if (a < b) r = m;
                else l = m;
            }
 
            for (int j = max(l-1, 0); j < min((int)ix[i].size(), 2 + max(0, r)); j++) {
                res = min(res, f(ix[i][j]) + memo[used |1<<i]);
            }
            res = min(res, f(0) + memo[used | 1<<i]);
            res = min(res, f(n) + memo[used | 1<<i]);
        }
    };
    ll ans;
    if (n > 10000) ans = exp_inv(n / 2) + exp_inv(n - n / 2);
    else ans = memo[0];
 
    cout << ans / 4;
    if (ans%4 == 1) cout << ".25";
    if (ans%4 == 2) cout << ".5";
    if (ans%4== 3) cout << ".75";
    cout << endl;
}

• Subtask 1: 5 / 5
• Subtask 2: 25 / 25
• Subtask 3: 30 / 30
• Subtask 4: 0 / 40