p501.ans1
======================
2

=================
p501.ans2
======================
8

=================
p501.cpp
======================
#include <bits/stdc++.h>

using namespace std;

template<typename T1, typename T2>
ostream& operator<<(ostream& out, const pair<T1, T2>& x) {
    return out << x.first << ' ' << x.second;
}

template<typename T1, typename T2>
istream& operator>>(istream& in, pair<T1, T2>& x) {
    return in >> x.first >> x.second;
}

template<typename T>
istream& operator>>(istream& in, vector<T>& a) {
    for(auto& x: a) {
        in >> x;
    }
    return in;
};

template<typename T>
ostream& operator<<(ostream& out, const vector<T>& a) {
    for(auto x: a) {
        out << x << ' ';
    }
    return out;
};

int n;
vector<string> layers;

void read() {
    cin >> n;
    layers.resize(2 * n);
    cin >> layers;
}

void solve() {
    // There are a ton of details in this problem, but in its core, it's a
    // dynamic programming. We simply need to avoid having too many states. In
    // particular, each of the 8 sides has n^2 cells, so for n=4 this is 128
    // cells and bitmask dp of 2^128 is clearly too slow.
    //
    // The octahedron has 8 triangular faces, 4 forming the top pyramid and 4
    // the bottom. Each face is divided into n^2 small triangles arranged in
    // rows of sizes 1, 3, 5, ..., 2n-1. Cells in each row alternate between
    // up-pointing and down-pointing. Adjacent cells (sharing an edge) can form
    // a domino, including across face boundaries and across consecutive rows.
    //
    // Key observation: between consecutive rows r and r+1, only up-pointing
    // cells in row r connect to down-pointing cells in row r+1. Per face there
    // are (r+1) such inter-row edges, giving 4*(r+1) "carry" cells total.
    // These carry cells are the only coupling between rows, so we can do a
    // layer-by-layer DP where the state is a bitmask of which carry cells are
    // still unmatched (need to be covered by a within-row domino in the next
    // row). The state size is 2^(4*r) which for n=4 is at most 2^16 = 65536.
    //
    // We solve the top and bottom pyramids independently. At the equator (the
    // boundary between the two halves), each pyramid's DP produces a count per
    // mask of unmatched equator cells. Two half-configurations are compatible
    // iff they have the exact same equator mask (an unmatched cell from above
    // pairs with the corresponding unmatched cell from below). So the answer
    // is the dot product of the two result vectors.

    vector<string> upper(n), lower(n);
    for(int i = 0; i < n; ++i) {
        upper[i] = layers[i];
    }
    for(int i = 0; i < n; ++i) {
        lower[i] = layers[2 * n - 1 - i];
    }

    auto solve_pyramid = [&](const vector<string>& rows) -> vector<int64_t> {
        int temp[1024 * 1024];
        int temp_size = 0;
        int first_row[16] = {};
        for(int mask = 0; mask < 16; ++mask) {
            for(int e = 0; e < 16; ++e) {
                int covered = mask;
                bool ok = true;
                for(int j = 0; j < 4 && ok; ++j) {
                    if(e & (1 << j)) {
                        int u = j, v = (j + 1) & 3;
                        if((covered >> u & 1) || (covered >> v & 1)) {
                            ok = false;
                        } else {
                            covered |= (1 << u) | (1 << v);
                        }
                    }
                }
                if(ok && covered == 15) {
                    first_row[mask]++;
                }
            }
        }

        int bit_mapping[5][32] = {};
        int bit_mapping_next[5][32];
        int bit_mapping_result[5][32];
        vector<int> next_row[4][1 << 12];
        int next_row_size[4][1 << 12] = {};
        int64_t dp[5][1 << 16] = {};

        memset(bit_mapping_next, -1, sizeof(bit_mapping_next));
        memset(bit_mapping_result, -1, sizeof(bit_mapping_result));

        for(int r = 0; r < n; ++r) {
            int cur_len = 2 * r + 1;
            int nxt_len = 2 * r + 3;
            int shift = 0, count = 0, current = 0;
            for(int g = 0; g < 4; ++g) {
                for(int i = 0; i < cur_len; i += 2) {
                    bit_mapping_next[r][current + i] = shift + (i + 1);
                    bit_mapping_result[r][current + i] = count++;
                }
                for(int i = 0; i < r; ++i) {
                    bit_mapping[r][g * r + i] = current + 2 * i + 1;
                }
                current += cur_len;
                shift += nxt_len;
            }
        }
        if(n > 0) {
            for(int i = 0; i < 32; ++i) {
                bit_mapping_next[n - 1][i] = 0;
            }
        }

        int row_mask[5] = {};
        for(int i = 0; i < n; ++i) {
            const string& a = rows[i];
            for(int j = 0; j < (int)a.size(); ++j) {
                if(a[j] == '*') {
                    row_mask[i] |= (1 << j);
                }
            }
        }

        auto carry_to_layer_mask = [&](int row, int cur_mask, int len) -> int {
            int res = 0;
            for(int i = 0; i < len; ++i) {
                if(cur_mask & (1 << i)) {
                    res |= (1 << bit_mapping[row][i]);
                }
            }
            return res;
        };

        auto enumerate_matchings = [&](auto&& self, int mask, int idx,
                                       int next_lvl_mask, int res, int len,
                                       int row) -> void {
            if(idx == len) {
                temp[temp_size++] = res;
                return;
            }
            if(mask & (1 << idx)) {
                self(self, mask, idx + 1, next_lvl_mask, res, len, row);
                return;
            }
            if(idx == 0 && ((mask & (1 << (len - 1))) == 0)) {
                self(
                    self, mask | (1 << (len - 1)), idx + 1, next_lvl_mask, res,
                    len, row
                );
            }
            if(bit_mapping_result[row][idx] != -1 &&
               ((next_lvl_mask & (1 << bit_mapping_next[row][idx])) == 0)) {
                self(
                    self, mask, idx + 1, next_lvl_mask,
                    res | (1 << bit_mapping_result[row][idx]), len, row
                );
            }
            if(idx < len - 1 && ((mask & (1 << (idx + 1))) == 0)) {
                self(self, mask, idx + 2, next_lvl_mask, res, len, row);
            }
        };

        for(int r = 1; r < n; ++r) {
            int prev_bits = 4 * r;
            for(int i = 0; i < (1 << prev_bits); ++i) {
                temp_size = 0;
                int cur_mask = carry_to_layer_mask(r, i, 4 * r);
                if((cur_mask & row_mask[r]) != 0) {
                    continue;
                }
                enumerate_matchings(
                    enumerate_matchings, cur_mask | row_mask[r], 0,
                    row_mask[r + 1], 0, 4 * (2 * r + 1), r
                );
                next_row[r][i].resize(temp_size);
                next_row_size[r][i] = temp_size;
                for(int j = 0; j < temp_size; ++j) {
                    next_row[r][i][j] = temp[j];
                }
            }
        }

        for(int i = 0; i < (1 << 4); ++i) {
            if((i & row_mask[0]) != 0) {
                continue;
            }
            if(n > 1 && (carry_to_layer_mask(1, i, 4) & row_mask[1]) != 0) {
                continue;
            }
            dp[1][i] += first_row[i | row_mask[0]];
        }

        for(int r = 1; r < n; ++r) {
            int prev_bits = 4 * r;
            for(int mask = 0; mask < (1 << prev_bits); ++mask) {
                if(dp[r][mask] == 0) {
                    continue;
                }
                for(int k = 0; k < next_row_size[r][mask]; ++k) {
                    int nxt = next_row[r][mask][k];
                    dp[r + 1][nxt] += dp[r][mask];
                }
            }
        }

        vector<int64_t> result(1 << (4 * n), 0LL);
        if(n == 0) {
            result[0] = 1;
        } else {
            for(int i = 0; i < (1 << (4 * n)); ++i) {
                if(i < (1 << 16)) {
                    result[i] = dp[n][i];
                }
            }
        }
        return result;
    };

    vector<int64_t> dp_up = solve_pyramid(upper);
    vector<int64_t> dp_down = solve_pyramid(lower);

    int64_t ans = 0;
    int final_size = 1 << (4 * n);
    for(int i = 0; i < final_size; ++i) {
        ans += dp_up[i] * dp_down[i];
    }
    cout << ans << '\n';
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int T = 1;
    // cin >> T;
    for(int test = 1; test <= T; test++) {
        read();
        solve();
    }

    return 0;
}

=================
p501.in1
======================
2
.***
........*...
************
....

=================
p501.in2
======================
3
....
************
....................
********************
............
****

=================
statement.txt
======================
501. Octahedron And Dominoes
Time limit per test: 0.25 second(s)
Memory limit: 262144 kilobytes
input: standard
output: standard

 Andrew has just made a breakthrough in puzzle making: he's invented a new puzzle that is both simple to understand and unlike everything that has been invented before. His new puzzle looks like an octahedron with each of its (triangular) faces split into n2 smaller triangles by 3(n-1) lines, n-1 parallel to each side of the face. Some of smaller triangles are black and some are white. The objective is to cover all white triangles with triangular dominoes without overlapping, leaving all black triangles uncovered. A triangular domino is two small triangles with one common side. Please note that a domino can cover one small triangle on a side of the octahedron and another on the adjacent side of the octahedron (in other words, you can bend your domino in the middle). You must place each domino so that it covers exactly two white small triangles (that means you can't cover some part of a triangle with one domino and the rest with another domino, for example). How many solutions does the given puzzle have?
Input
The first line of the input file contains an integer n (1 ≤ n ≤ 4). The next 2n lines describe which small triangles are black and which are white. Imagine the octahedron standing on its vertex, with one of its other vertices pointing on us. Then the small triangles can be split into horizontal layers. The topmost layer contains 4 triangles, one per each side that ends in the top vertex. The next layer contains 12 triangles, 3 per each side that ends in the top vertex, and so on. The size of each layer increases by 8 until it reaches 8n-4 in the middle, then the next layer is again of 8n-4 small triangles (here we switched from the top 4 faces to the bottom 4 faces), and then the size of each next layer is less by 8 until we reach the bottommost layer that has just 4 triangles. The octrahedron is given layer-by-layer, and each layer is started with the leftmost small triangle on the visible part of the octahedron (the four "front" faces), goes from left to right along the visible part, and then switches to the invisible part and goes back from right to left. One layer is highlighted on the picture above. Each small triangle is specified either by '.', denoting a white triangle, or by '*', denoting a black triangle.
Output
Output one integer — the number of possible coverings of white triangles of the given octahedron with triangular dominoes.
Example(s)
sample input
sample output
2
.***
........*...
************
....
2

sample input
sample output
3
....
************
....................
********************
............
****
8


=================
