E - Christmas Color Grid 1

https://atcoder.jp/contests/abc334/tasks/abc334_e

思路

https://www.cnblogs.com/Lanly/p/17923753.html

Code

https://atcoder.jp/contests/abc334/submissions/49243194

int h,w;
bool s[1005][1005];
int c[1005][1005]; // c - class
long long modbase = 998244353;

struct NODE{
    int x;
    int y;
};

vector<struct NODE> directions = {
    {1, 0},
    {-1, 0},
    {0, 1},
    {0, -1}
};

void dfs(int i, int j, int class_order){
    if (i<1 || i>h){
        return;
    }
    
    if (j<1 || j>w){
        return;
    }

    bool sij = s[i][j];
    if (sij == false){
        return;
    }
    
    if (c[i][j] > 0){
        return;
    }
    
    c[i][j] = class_order;
    
    for(int k=0; k<directions.size(); k++){
        struct NODE nd = directions[k];
        int ni = i + nd.x;
        int nj = j + nd.y;
        
//        cout << "ni = " << ni << ", nj=" << nj << endl;
        
        dfs(ni, nj, class_order);
    }
}

int get_nb_comp_num(int i, int j){
    if (i<1 || i>h){
        return 0;
    }

    if (j<1 || j>w){
        return 0;
    }

    bool sij = s[i][j];
    if (sij == true){
        return 0;
    }

    set<int> nbs;
    for(int k=0; k<directions.size(); k++){
        struct NODE nd = directions[k];
        int ni = i + nd.x;
        int nj = j + nd.y;

        if (ni >= 1 && ni <=h && nj >= 1 && nj <= w){
            bool sninj = s[ni][nj];
            if (sninj == true){
                nbs.insert(c[ni][nj]);
            }
        }
    }
    
    return nbs.size();
}

long long qpower(long long a, long long b) {

    long long qwq = 1;

    while (b) {

        if (b & 1)

            qwq = qwq * a % modbase;

        a = a * a % modbase;

        b >>= 1;

    }

    return qwq;

}

long long inv(long long x) { return qpower(x, modbase - 2); }

int main()
{
    cin >> h >> w;
    
    for(int i=1; i<=h; i++){
        for(int j=1; j<=w; j++){
            char ch;
            cin >> ch;
            if (ch == '#'){
                s[i][j] = true;
            } else {
                s[i][j] = false;
            }
        }
    }

//    cout << "--- after input ------" << endl;

    int class_order = 0;
    for(int i=1; i<=h; i++){
        for(int j=1; j<=w; j++){
            bool sij = s[i][j];
            if (sij == true && c[i][j] == 0){
//                cout << "i = " << i << ", j=" << j << endl;
                class_order++;
                dfs(i, j, class_order);
            }
        }
    }
    
//    for(int i=1; i<=h; i++){
//        for(int j=1; j<=w; j++){
//            int cij = c[i][j];
//            cout << cij << " ";
//        }
//        cout << endl;
//    }

//    cout << "--- after dfs ------" << endl;

    long long redcnt = 0;
    long long compcnt = 0;
    for(int i=1; i<=h; i++){
        for(int j=1; j<=w; j++){
            bool sij = s[i][j];
            if (sij == false){
//                cout << "comp cnt for i=" << i << ", j=" << j << endl;
                redcnt++;
                
                int nbcmpnum = get_nb_comp_num(i, j);
//                cout << "nbcmpnum = " << nbcmpnum << endl;
                compcnt += class_order - nbcmpnum + 1;
            }
        }
    }
    
//    cout << "--- after compcnt ------" << endl;
//    
//    cout << "compcnt = " << compcnt << ", redcnt=" << redcnt << endl;

//    long long ret = compcnt / redcnt;
    long long ret = compcnt % modbase * inv(redcnt) % modbase;
    cout << ret << endl;

    return 0;
}