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  1. Prepare
  2. Algorithms
  3. Dynamic Programming
  4. Lego Blocks
  5. Discussions

Lego Blocks

  • dehaka
     + 2 comments

    O(n * m^2), strange this passed, since it requires at least 1 billion operations. can be modified to O(t*n*m) by calculating each height individually in response to the query, instead of calculating all 1 <= n <= 1000

    there's probably a O(n* m) algo by finding a constant time method to calculate the number of bad layouts of length m+1 from smaller length bad layouts, but this O(n* m^2) algo already pass all tests so i cant be bothered

    void legoBlocks(vector<vector<long>>& total, vector<vector<long>>& bad) {
    vector<long> oneRow = { 0, 1, 2, 4, 8 };
    for (int i = 5; i <= 1000; i++) oneRow.push_back((oneRow[i-1] + oneRow[i-2] + oneRow[i-3] + oneRow[i-4]) % 1000000007);
    total.push_back(oneRow);
    for (int i = 2; i <= 1000; i++) {
        total.emplace_back();
        for (int j = 0; j <= 1000; j++) total.back().push_back((oneRow[j] * total[i-1][j]) % 1000000007);
    }
    for (int n=1; n <= 1000; n++) {
        bad.emplace_back(vector<long>{0, 0});
        for (int m=2; m <= 1000; m++) {
            long temp = 0;
            for (int i=1; i < m; i++) temp = (temp + total[n][i] * (total[n][m-i] - bad[n][m-i])) % 1000000007;
            bad[n].push_back(temp);
        }
    }
}

int main()
{
    int t, n, m;
    vector<vector<long>> total = {vector<long>(1001)}, bad = {vector<long>(1001)};
    legoBlocks(total, bad);
    cin >> t;
    for (int i=1; i <= t; i++) {
        cin >> n >> m;
        cout << (total[n][m] - bad[n][m] + 1000000007) % 1000000007 << '\n';
    }
}