提出 #50637204

---

ソースコード 拡げる

#include <bits/stdc++.h>
#include <atcoder/modint>
#include <atcoder/segtree>

using Num = int;
using Numeric = double;

Numeric apply(Numeric a, Numeric b) {
    return a + b;
}

Numeric unit() {
    return 0;
}

void solve(std::istream& is, std::ostream& os) {
    Num n, l, d;
    is >> n >> l >> d;

    using SegTree = atcoder::segtree<double, std::plus<>{}, [] { return 0; }>;
    const Num size = n + 1;
    SegTree tree_dealer(size);
    tree_dealer.set(0, 1.0);

    for(Num i{1}; i<=n; ++i) {
        Num left = std::max(0, i-d);
        Num right = std::min(i, l);
        if (left < right) {
            const auto p = tree_dealer.prod(left, right) / d;
            tree_dealer.set(i, p);
        }
    }

    std::vector<Numeric> win_player(size);
    for(Num i{0}; i<=n; ++i) {
        win_player.at(i) = 1.0 - tree_dealer.prod(std::max(i, l), size);
    }

    std::vector<Numeric> cumsum {0.0};
    for(Num i{0}; i<=n; ++i) {
        const auto hit = (cumsum.back() - cumsum.at(std::max(i-d, 0))) / d;
        const auto stand = win_player.at(n-i);
        const auto p = cumsum.back() + std::max(hit, stand);
        cumsum.push_back(p);
    }

    os << std::setprecision(20) << (cumsum.back() - cumsum.at(cumsum.size() - 2)) << "\n";
}

int main(void) {
    solve(std::cin, std::cout);
    return 0;
}

提出情報

ジャッジ結果