Submission #723247

#	Time	Username	Problem	Language	Result	Execution time	Memory
723247		drdilyor	Boarding Passes (BOI22_passes)	C++17	5 / 100	90 ms	664 KiB

passes

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

ll exp_inv(ll x) {
    return x * (x-1);
}

int main() {
    char a = 'A';
    string s; cin >> s;
    const int G = 10;
    int n = s.size();
    if (n == 1) {
        cout << "0\n";
        return 0;
    }

    vector memo(1<<G, (ld)-1);

    auto suml = [&](int c1, int c2, int l, int r) {
        ll cur = 0, res = 0;
        for (int i = l; i <= r; i++) {
            if (s[i] == c1+a) res += cur;
            if (s[i] == c2+a) cur++;
        }
        return res;
    };
    auto sumr = [&](int c1, int c2, int l, int r) {
        ll cur = 0, res = 0;
        for (int i = r; i >= l; i--) {
            if (s[i] == c1+a) res += cur;
            if (s[i] == c2+a) cur++;
        }
        return res;
    };

    auto dp = [&](auto& dp, int used)->ld{
        if (memo[used] >= 0) return memo[used];
        if (__builtin_popcount(used) == G) return 0;
        vector has(n, 0);
        for (int j = 0; j < n; j++) {
            if (used& 1<<(s[j] - a))
                has[j] = 1;
        }

        ld res = 1e18;
        for (int i = 0 ;i < G; i++) {
            ld cur = 1e18;
            if (used&1<<i) continue;
            vector<ld> left(n), right(n);
            int c = 0;
            for (int j = 0; j < n; j++) {
                if (s[j] == i + a)
                    c++;
                ll sum = 0;
                for (int c2 = 0; c2 < G; c2++)
                    if (used&1<<i)
                        sum+= suml(i, c2, 0, j);
                left[j] = sum * 4 + exp_inv(c);
            }

            c = 0;
            for (int j = n-1; j >= 0; j--) {
                if (s[j] == i + a)
                    c++;
                ll sum = 0;
                for (int c2 = 0; c2 < G; c2++)
                    if (used&1<<i)
                        sum += sumr(i, c2, j, n-1);

                right[j] = sum * 4 + exp_inv(c);
            }

            for (int mid = 1; mid < n; mid++) {
                cur = min(cur, left[mid-1] + right[mid]);
            }
            res = min(res, cur + dp(dp, used |1<<i));
        }
        return memo[used] = res;
    };
    ll ans;
    if (n > 10000) ans = exp_inv(n / 2) + exp_inv(n - n / 2);
    else ans = dp(dp, 0);

    cout << ans / 4;
    if (ans%4 == 1) cout << ".25";
    if (ans%4 == 2) cout << ".5";
    if (ans%4== 3) cout << ".75";
}

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