Submission #538272

#	Time	Username	Problem	Language	Result	Execution time	Memory
538272		four_specks	Collecting Mushrooms (NOI18_collectmushrooms)	C++17	100 / 100	25 ms	12684 KiB

mushrooms

#include <bits/stdc++.h>

using namespace std;

inline namespace
{
} // namespace

/*
    - use 2D prefix sums to find number of sprinklers covering a square
 */

void solve()
{
    int r, c, d, k;
    cin >> r >> c >> d >> k;

    vector pref(r + 1, vector(c + 1, 0));

    vector grid(r, vector<bool>(c, 0));
    for (int i = 0; i < r; i++)
    {
        for (int j = 0; j < c; j++)
        {
            char s;
            cin >> s;

            if (s == 'S')
            {
                pref[max(0, i - d)][max(0, j - d)]++;
                pref[max(0, i - d)][min(c, j + d + 1)]--;
                pref[min(r, i + d + 1)][max(0, j - d)]--;
                pref[min(r, i + d + 1)][min(c, j + d + 1)]++;
            }
            else if (s == 'M')
                grid[i][j] = 1;
        }
    }

    vector a(r + 2, vector(c + 2, 0));
    for (int i = 0; i <= r; i++)
    {
        for (int j = 0; j <= c; j++)
            a[i + 1][j + 1] = a[i + 1][j] + a[i][j + 1] - a[i][j] + pref[i][j];
    }

    int cnt = 0;
    for (int i = 0; i < r; i++)
    {
        for (int j = 0; j < c; j++)
        {
            if (grid[i][j] && a[i + 1][j + 1] >= k)
                cnt++;
        }
    }

    cout << cnt << '\n';
}

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

    solve();

    return 0;
}

• Subtask 1: 9 / 9
• Subtask 2: 10 / 10
• Subtask 3: 18 / 18
• Subtask 4: 23 / 23
• Subtask 5: 19 / 19
• Subtask 6: 21 / 21