Submission #48810510

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Source Code Expand

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

namespace {
    using ModInt [[maybe_unused]] = atcoder::modint998244353;
    using Num [[maybe_unused]] = long long int;
    using Vec [[maybe_unused]] = std::vector<Num>;
    using Set [[maybe_unused]] = std::set<Num>;
    using Mset [[maybe_unused]] = std::multiset<Num>;
    using Edges [[maybe_unused]] = std::vector<std::vector<Num>>;

    template<typename T>
    using Q [[maybe_unused]] = std::queue<T>;

    template<typename T>
    using PQ [[maybe_unused]] = std::priority_queue<T, std::vector<T>, std::greater<T>>;
}

Num h, w;
bool grid[1024][1024];

Num to_index(Num y, Num x) {
    return y*w + x;
}

void solve(std::istream& is, std::ostream& os) {
    is >> h >> w;

    Num n_red {0};
    for(Num y{0}; y<h; ++y) {
        std::string s;
        is >> s;
        for(Num x{0}; x<w; ++x) {
            bool g = s.at(x) == '#';
            grid[y][x] = g;
            n_red += (g == false);
        }
    }

    const std::vector<std::pair<Num, Num>> dyxs = {{1,0}, {-1,0}, {0,1}, {0,-1}};
    atcoder::dsu tree(h*w);
    for(Num y{0}; y<h; ++y) {
        for(Num x{0}; x<w; ++x) {
            for(const auto& [dy, dx] : dyxs) {
                const Num ty = y + dy;
                const Num tx = x + dx;
                if ((ty >= 0) && (ty < h) && (tx >= 0) && (tx < w)) {
                    if (grid[y][x] && grid[ty][tx]) {
                        tree.merge(to_index(y,x), to_index(ty,tx));
                    }
                }
            }
        }
    }

    Num total {0};
    for(const auto& vec : tree.groups()) {
        const auto pos = vec.at(0);
        const Num y = pos / w;
        const Num x = pos % w;
        if (grid[y][x]) {
            total += 1;
        }
    }

    Num diff {0};
    for(Num y{0}; y<h; ++y) {
        for(Num x{0}; x<w; ++x) {
            if (grid[y][x]) {
                continue;
            }

            std::set<int> groups;
            for(Num i{0}; i<4; ++i) {
                const auto& [dyi, dxi] = dyxs.at(i);
                const Num tyi = y + dyi;
                const Num txi = x + dxi;
                if (grid[tyi][txi] && (tyi >= 0) && (tyi < h) && (txi >= 0) && (txi < w)) {
                    groups.insert(tree.leader(to_index(tyi,txi)));
                }
            }

            const Num size = static_cast<Num>(groups.size());
            if (size > 1) {
                diff += size - 1;
            } else if (size == 0) {
                diff -= 1;
            }
        }
    }

    ModInt answer = total;
    ModInt p = diff;
    p /= n_red;
    answer -= p;
    os << answer.val() << "\n";
}

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

Submission Info

Judge Result