c++ using bfs (breath first search) approach

define pii pair

define mk make_pair

int bfs(int r, int c, vector> &mat, vector> &vis, int n, int m) { int surf = 0; queue q; q.push(mk(r,c)); // cout << "starting " << r << " "<

pii cur;
while (!q.empty()) {
    cur = q.front();
    int cr = cur.first;
    int cc = cur.second; 
    q.pop();

    if (!vis[cr][cc]) {
        vis[cr][cc]=true;
        // cout << "visiting " << cr << " " << cc << '\n';
        surf++;

        if (cr-1 >= 0) {
            if (mat[cr-1][cc]) q.push(mk(cr-1,cc));

            if (cc-1 >= 0 and mat[cr-1][cc-1]) q.push(mk(cr-1,cc-1));

            if (cc+1 < m and mat[cr-1][cc+1]) q.push(mk(cr-1,cc+1));
        }
        if (cr+1 < n) {
            if (mat[cr+1][cc]) q.push(mk(cr+1,cc));

            if (cc-1 >= 0 and mat[cr+1][cc-1]) q.push(mk(cr+1,cc-1));

            if (cc+1 < m and mat[cr+1][cc+1]) q.push(mk(cr+1,cc+1));
        }
        if (cc-1 >= 0) {
            if (mat[cr][cc-1]) q.push(mk(cr,cc-1));

            // if (cr-1 >= 0 and mat[cr-1][cc-1]) q.push(mk(cr-1,cc-1));

            // if (cr+1 < m and mat[cr+1][cc+1]) q.push(mk(cr+1,cc+1));
        }
        if (cc+1 < m) {
            if (mat[cr][cc+1]) q.push(mk(cr,cc+1));

            // if (cr-1 >= 0 and mat[cr-1][cc+1]) q.push(mk(cr-1,cc+1));
            // 
            // if (cc+1 < m and mat[cr-1][cc+1]) q.push(mk(cr-1,cc+1));
        }
    }
}

return surf;

}

int connectedCell(vector> matrix) { int n = matrix.size(), m = matrix[0].size(); vector> vis(n, vector(m,false));

int res = 0;

for (int i = 0; i < n; i++) {
    for (int j = 0; j < m; j++) {
        if (matrix[i][j] and !vis[i][j]) {
            res = max(res,bfs(i,j,matrix,vis,n,m));
        }
    }
}
return res;

}