D. ZZPooling 密碼池產生器 (zzpooling)

#include <bits/stdc++.h>
using namespace std;

int main() {
    // ios_base::sync_with_stdio(0), cin.tie(0);

    string S; getline(cin, S);
    int N; cin >> N;
    char zigzag, pooling; cin >> zigzag >> pooling;
    int poolsz; cin >> poolsz;

    if (zigzag == 'b') reverse(begin(S), end(S));

    vector<string> board(N);
    for (int i = 0; i < N; ++i) board[i] = S.substr(i*N, N);

    auto valid = [&](int r, int c) -> bool {
        return (0 <= r and r < N and 0 <= c and c < N);
    };

    string zigstr;
    for (int sum = 0; sum <= 2*N-2; ++sum) {
        if (sum & 1) {for (int r = 0, c = sum; c >= 0; ++r, --c) if (valid(r, c)) zigstr += board[r][c];}
        else         {for (int c = 0, r = sum; r >= 0; ++c, --r) if (valid(r, c)) zigstr += board[r][c];}
    }

    for (int i = 0; i < N; i += poolsz) {
        for (int j = 0; j < N; j += poolsz) {
            int mx = 0, sum = 0;
            for (int x = 0; x < poolsz; ++x) {
                for (int y = 0; y < poolsz; ++y) {
                    mx = max(mx, (int)zigstr[(i+x)*N + (j+y)]);
                    sum += zigstr[(i+x)*N + (j+y)];
                }
            }
            cout << (char)(pooling == 'a' ? sum / poolsz / poolsz : mx);
        }
    }
    cout << "\n";

    return 0;
}